Mensajero Estelar No. 71 Julio

SOVAFA
ACA
Sociedad Venezolana
de Aficionados a la
Astronomía
Asociación Carabobeña de
Astronomía
Mensajero
Estelar
Año 38
Nº 71
Julio - Septiembre de 2014
Contenido
1.- Noticias
2.- Radiantes del Trimestre
3.- Fases de la Luna
4.- Ocultación de Marte, Jul. 06
5.- Luz Solar y Tensión sanguínea
6.- El Niño 2014
7.- Colapso de Hielo en Plataforma Antártica W
8.- Optical Response of the atmosphere during…
9.- Punto de Inflexión
www.sovafa.com,
www.sovafa.org
@sovafa,
10.- Evidence of Solar Wind modulatión of…
11.- Planetas Acuosos
12.- El Almanaque Nautico y el Aficionado
13.- El Niño Histórico en Venezuela
14.- Lado Oculto de la Luna…
15.- Alberto Ramos
16.- Seminario: Los Métodos de la Ciencia
17.- Primera evidencia directa de la Inflación
18.- Reporte de Observación Eclipse Lunar
@astrorecord,
[email protected]
Noticias
1.- El lago Superior continúa con un alto porcentaje de hielo en Mayo 05 de 2014. Este año la superficie del lago se
cubrió de hielo en un 95,1% y ahora esta es de un 59,7%, el año pasado el hielo desapareció completamente el 12 de abril.
Esto al parecer se debe a vientos polares que han hecho que las temperaturas promedios en la zona estén muy por debajo
de la media para estos meses.
2.- El 18 de Agosto ocurrirá una conjunción entre Venus y Júpiter. La separación entre ambos cuerpos será de 15´ de
arco, media Luna. La máxima aproximación ocurrirá a las 05:00 GMT.
3.- Este año parece que se formará El Niño. Las mediciones de la superficie del agua superficial en el Pacífico parecen
indicarlo. De Aparecer será entre Junio y Julio de 2014.
4.- Un gigantesco glaciar 8 veces mayor que la isla de Manhattan y bautizado como B31 se desprendió del Glaciar de
Pine Island, en la Antártica y flota a la deriva en el Océano Glaciar Antártico.
5.- Meteorólogos descubren que la aparición de nubes noctulicentes se ha incrementado entre 2002 y 2012, pero aún no es
claro a qué se debe este fenómeno.
6.- Confirmado el elemento 117 de la tabla periódica, bautizado como Ununseptio, con una vida media de millonésimas
de segundo.
7.- La zona ecológica alrededor de las estrellas podría ser más grande que lo que se había considerado hasta ahora, en
especial en regiones alrededor de estrellas enanas. Esto eleva la posibilidad de la vida en el Universo.
8.- Según observaciones realizadas por los hermanos Carlos y Raúl de la Fuente Marcos, especialistas en dinámica orbital
de la Universidad Complutense de Madrid, podrían existir 2 planetas gigantes más allá de la órbita de Plutón. Esto lo
creen debido a extraños patrones orbitales de 2 objetos transplutonianos. El primero de estos planetas tendría un tamaño
entre el de Marte y Saturno y se encontraría a 200 UA, el otro tendría una órbita resonante con este y estaría a 250 UA.
9.- Utilizando la interferometría con dos radiotelescopios, el Dr. Roger Deane de Sur África detecto 3 Agujeros Negros
Supermasivos que orbitan en torno a un centro de masa común en el núcleo de una galaxia espiral a más de 4.000
millones de Años Luz de la nuestra.
10.- Un equipo de astrónomos descubrió una estrella enana blanca muy fría, con temperaturas del orden de los 3.000º K,
la más fría detectada hasta el momento. Esta orbita alrededor del Pulsar PSR J2222 – 0137 cada 2,5 días. Lo interesante
en ella es que su temperatura es tan baja que el Carbóno en ella debe haberse cristalizado convirtiéndola en un diamante
del tamaño de nuestro planeta.
11.- El 5 de junio la NASA probó un instrumento de comunicación a base de luz llamado OPALS (Optical Payload for
Lasercomm Sciences), en el que desde la Estación Espacial Internacional se envió datos a Tierra. El Nuevo instrumento
es unas 1.000 veces más veloz que sus predecesores, que usaban ondas de radio. Con este nuevo instrumento se envió 50
Mega Bites de información por segundo.
12.- Una fuerte oleada de calor precede al Monzón en India este año. Las temperaturas en el Sub Continente Asiático y
otros lugares de Asia fueron registros records, llegando a mantenerse sobre los 43º C por días.
13.- Este 30 de Junio se cumplió una década desde que la sonda Cassini arribó al Sistema de Saturno, ha sido una década
de descubrimientos que tienen que ver con Biología, dinámica atmosférica, Mecánica, y otras ciencias.
14.- El Curiosity cumplió un año marciano sobre la superficie de este planeta el día 24 de Junio. En este año de 687 días
Curiosity ha estudiado suelo, rocas, luz, clima, y atmósfera de Marte.
15.- El estudio de las galaxias enanas del Universo ha demostrado que estas contribuyeron mucho más que lo que se cree
en la formación de estrellas en el Universo Temprano.
16.- El Satélite QuickScat enviado para una misión de tres años de estudio de los patrones de circulación oceánica,
cumplió 15 años de servicio este 19 de junio pasado. Han sido 15 años de datos que han fortalecido el conocimiento de la
circulación atmosférica y de corrientes marinas en el planeta.
17.- Gigantescos Sprites fueron fotografiados en el Oeste de USA. Estos alcanzaron alturas colosales después de cada
descarga eléctrica de una gran tormenta, alcanzando 46 millas de altura.
INVITACIÓN
Este nuevo número del Mensajero posee trabajos de astrónomos profesionales como el Dr. Marcos Peñalosa;
Drs. C J Scott, R G Harrison, M J Owens, M Lockwood and L Barnard, Penn State University, NASA, y otros. Son
trabajos muy interesantes que le dan realce a nuestro boletín, pero a parte de los trabajos de cálculo del Ingeniero Carlos
Gil de ACA, y los escritos de Jesús Otero, pocos son los miembros de SOVAFA y ACA que han contribuido a nuestro
Mensajero. No es necesario escribir un tratado científico, basta con una observación, un artículo divulgativo, una
actividad astronómica.
Anímate y escribe algo en nuestro Mensajero.
Lluvias de Estrellas del Trimestre
Radiante
α Oriónidas
Capricórnidas
Nu Geminíadas
Fecha
Jul. 09 - 25
Jun. 04 – Ago. 2
Jul. 09 - 18
Máximo
Jul. 12
Jul. 18
Jul. 12
T.H.Z.
50
10
60
α
05h 42m
20h 44m
06h 32m
δ
12°
.- 14°
21º
Lamda Geminiadas
Perseidas
31 Vulpecúlidas
Corona Austrálidas
Jul. 04 - 29
Jul. 20 – Ago. 23
Sep.
Sep. 29
Jul. 12
Ago. 12 - 13
30
80 - 120
07h 20m
03h 00m
13º
58°
Sept. 29
¿?
18h 33m
.- 37°
Hora
04:30
22:00
02:00
20:00
19:00
Las lluvias de estrellas aquí listadas se encuentran todas activas, algunas de ellas son de difícil observación pues
sus meteoros son de poco brillo.
Hay que ver cuál es la fase lunar el día de la observación, pues la luz de la Luna puede afectar mucho la
observación del radiante.
Máximo es el día en que se espera que la lluvia de estrellas llegue a su máximo número de meteoros.
THZ es el número de meteoros que veríamos del radiante si este se encontrara en el zenit.
α y δ son Ascensión Recta y Declinación.
Hora se refiere a la hora en la cual puede empezar a observarse el radiante. Viene en Hora Legal de Venezuela.
Las Perseidas son uno de los radiantes meteóricos más interesantes del año, dan un buen número de meteoros
brillantes, son rápidos, y algunos dejan estelas.
Las Vulpecúlidas es un radiante que produjo un número importante de Meteoros el AÑO PASADO, no está
catalogado. Fue descubierto por Jesús Otero. No se da coordenadas, fechas de máximo, THZ, ni posición, debido a que
solo se le observó por una hora y se desconoce si este radiante es un nuevo radiante o es un radiante esporádico. Urgen
observaciones sobre esta lluvia de estrellas. La Luna interferirá con la observación entre el 5 y el 13 de septiembre, pero
el resto del mes podrá realizarse observaciones de al menos 2 horas.
Las Un Geminíadas son muy difíciles de observar desde Venezuela, así como las Lambda Geminíadas. Esto es mejor
observarlo con radar.
Si observa cualquiera de estos radiantes o una actividad meteórica inusual envíe un informe a
[email protected] o un mensaje al Twitter: αastrorecord
Fases de la Luna

Luna Nueva
Fecha
Hora
Jun. 27
08:09
Jul. 26 22:42
Ago. 25 14:12
Sep. 24 06:12

Cuarto Creciente
Fecha
Hora
Jul. 05 11:59
Ago. 04 00:50
Sep. 02 11:11
Oct. 01 19:32

Luna Llena
Fecha
Hora
Jul. 12 11:25
Ago. 10 18:10
Sep. 09 01:38
Oct. 08 10:49 t

Cuarto Menguante
Fecha Hora
Jul.19 02:08
Ago. 17 12:26
Sep. 16 02:05
Oct. 15 19:12
En Luna Nueva la Luna no se puede ver, pues está en Conjunción con el Sol.
En Cuarto Creciente la Luna se observa en la tarde y primeras horas de la noche.
En Luna Llena la Luna sale al ocultarse el Sol y se observa durante toda la noche.
En Cuarto Menguante la Luna sale tarde, se observa de madrugada y primeras horas de la mañana.
Estos datos son muy importantes a la hora de planificar sus observaciones, ya sean planetarias, de radiantes, u
objetos de espacio profundo.
Téngalas en cuenta para la observación de eventos astronómicos.
t = Eclipse Total de Luna
El Eclipse Total de Luna de Oct. 08 podrá observarse en el momento de la totalidad desde Venezuela. Este es un proyecto
importante de observación y estamos involucrados en un proyecto internacional.
Estén pendientes de consultar: www.sovafa.com y leer el manual de observación de Eclipses Lunares.
Ocultación de Marte, Jul. 06.
El día 06 de Julio ocurrirá una ocultación del planeta Marte por la Luna, que será visible en casi toda Venezuela,
excluyendo al Norte de Zulia, y los estados Falcón, Distrito Capital, Vargas, y Nueva Esparta.
Ocultación y Aparición de Marte en T.U. para ciudades de Venezuela en Jul.05, 2014
Datos tomados de IOTA
International Ocultation and Timming Asociation
Desaparición
Ciudad
268
269
270
271
272
273
274
275
276
277
278
279
280
281
282
283
284
285
286
287
288
289
290
291
292
293
294
295
296
297
298
299
300
301
302
303
304
305
306
307
308
309
VE
VE
VE
VE
VE
VE
VE
VE
VE
VE
VE
VE
VE
VE
VE
VE
VE
VE
VE
VE
VE
VE
VE
VE
VE
VE
VE
VE
VE
VE
VE
VE
VE
VE
VE
VE
VE
VE
VE
VE
VE
VE
h
Acarigua
Anaco
Barcelona
Barinas
Barquisimeto
Caicara De Orinoco
Calabozo
Canaima
Carora
Carrizal
Ciudad Bolivar
Cumana
El Dorado
Elorza
Guanare
Guasdualito
Guayana
Higuerote
La Fria
Maracaibo
Maracaibo
Maracay
Maturin
Merida
Palmarito
Puerto Ayacucho
Puerto Cabello
San Antonio
San Carlos
San Cristobal
San Felipe
San Fernando De Apure
San Fernando Deatabapo
San Juan De Los Morros
San Tome
Santa Barbara
Santo Domingo
Tucupita
Tumeremo
Valencia
Valera
Valle De La Pascua
m
2
2
2
2
2
2
2
2
2
2
2
2
2
2
2
2
2
2
2
2
2
2
2
2
2
2
2
2
2
2
2
2
2
2
2
2
2
2
2
2
2
2
U.T. Sun Moon
s Alt Alt Az
34
41
45
28
37
33
35
35
36
37
38
50
37
26
31
23
39
47
22
35
41
42
45
26
25
26
44
21
36
21
40
31
24
40
40
25
21
43
38
40
30
38
26
52
41
39
13
16
7
19
35
52
26
10
38
2
2
45
53
38
47
47
52
19
16
38
46
57
0
25
15
54
22
47
53
9
17
56
40
18
46
56
39
42
33
26
25
35
32
30
31
27
33
30
27
24
25
36
34
37
25
26
39
34
29
29
24
37
36
34
29
39
32
39
31
32
35
29
27
37
39
24
25
30
35
29
CA
o
253
256
255
253
253
255
254
257
253
255
256
256
257
254
253
254
256
255
252
252
254
254
256
253
254
256
254
252
254
252
254
255
257
254
256
252
253
256
257
254
253
255
PA
o
17N
16N
8N
25N
12N
29N
21N
36N
11N
17N
25N
2N
33N
34N
22N
34N
24N
3N
29N
8N
8N
8N
12N
26N
31N
40N
4N
31N
15N
31N
8N
28N
47N
12N
20N
24N
33N
18N
30N
9N
20N
18N
WA
o
39
38
30
47
34
51
43
58
33
39
47
24
55
56
44
56
46
25
51
30
31
30
35
48
53
62
26
53
37
53
30
50
69
34
42
46
55
41
53
31
42
40
a
m/o
15
14
7
23
10
27
19
34
9
15
24
1
32
32
20
32
23
1
27
6
7
6
11
24
30
38
2
30
14
30
7
26
46
10
18
22
31
17
29
7
18
16
b
m/o
+2.0
+1.4
+1.3
+2.1
+2.1
+1.6
+1.8
+1.3
+2.3
+1.7
+1.3
+9.9
+1.2
+2.0
+2.1
+2.2
+1.2
+9.9
+2.4
+9.9
+1.9
+1.9
+1.2
+2.3
+2.1
+1.8
+9.9
+2.4
+2.0
+2.4
+2.1
+1.8
+1.8
+1.8
+1.3
+2.4
+2.3
+1.1
+1.1
+1.9
+2.2
+1.6
+5.1
+4.8
+8.2
+3.4
+7.3
+2.5
+3.9
+1.7
+8.0
+4.8
+2.8
+9.9
+1.9
+2.1
+4.0
+2.2
+2.9
+9.9
+2.9
+9.9
+8.9
+9.7
+5.8
+3.3
+2.4
+1.5
+9.9
+2.6
+5.5
+2.5
+9.6
+2.7
+1.0
+6.7
+3.8
+3.7
+2.4
+3.9
+2.1
+8.5
+4.5
+4.4
Reaparicion
Ciudad
268
269
270
271
VE
VE
VE
VE
h
Acarigua
Anaco
Barcelona
Barinas
m
3
3
3
3
U.T. Sun Moon
s Alt Alt Az
3 5
9 7
3 43
7 22
26
20
21
26
256
257
257
256
CA
o
PA
o
WA
o
a
m/o
b
m/o
-25N 357 333 +1.1 -7.0
-26N 356 332 +1.1 -6.6
-19N
3 339 +9.9 +9.9
-32N 350 326 +1.1 -5.3
Reaparicion
Ciudad
272
273
274
275
276
277
278
279
280
281
282
283
284
285
286
287
288
289
290
291
292
293
294
295
296
297
298
299
300
301
302
303
304
305
306
307
308
309
VE
VE
VE
VE
VE
VE
VE
VE
VE
VE
VE
VE
VE
VE
VE
VE
VE
VE
VE
VE
VE
VE
VE
VE
VE
VE
VE
VE
VE
VE
VE
VE
VE
VE
VE
VE
VE
VE
h
Barquisimeto
Caicara De Orinoco
Calabozo
Canaima
Carora
Carrizal
Ciudad Bolivar
Cumana
El Dorado
Elorza
Guanare
Guasdualito
Guayana
Higuerote
La Fria
Maracaibo
Maracaibo
Maracay
Maturin
Merida
Palmarito
Puerto Ayacucho
Puerto Cabello
San Antonio
San Carlos
San Cristobal
San Felipe
San Fernando De Apure
San Fernando Deatabapo
San Juan De Los Morros
San Tome
Santa Barbara
Santo Domingo
Tucupita
Tumeremo
Valencia
Valera
Valle De La Pascua
m
2
3
3
3
2
3
3
3
3
3
3
3
3
2
3
2
2
2
3
3
3
3
2
3
3
3
2
3
3
3
3
3
3
3
3
2
3
3
U.T. Sun Moon
s Alt Alt Az
59
16
8
24
57
6
17
0
24
15
5
13
17
57
7
51
59
58
8
6
12
22
55
8
3
9
57
14
26
2
12
3
10
13
22
59
2
8
4
34
52
51
15
46
8
8
17
24
40
22
10
22
2
27
41
47
27
28
26
21
17
37
5
7
22
7
37
36
17
29
19
40
34
36
52
44
27
20
23
15
28
23
17
21
14
24
26
25
16
24
28
31
25
25
19
27
25
20
26
28
25
28
27
22
20
24
19
28
27
16
14
25
27
21
255
258
257
259
255
257
258
256
259
257
256
257
259
256
256
253
256
255
258
256
257
259
255
256
256
256
255
258
259
256
258
255
256
258
259
255
255
257
CA
o
PA
o
-20N
-39N
-30N
-48N
-18N
-27N
-37N
-13N
-46N
-42N
-29N
-41N
-36N
-12N
-35N
-14N
-18N
-17N
-24N
-33N
-39N
-50N
-13N
-38N
-24N
-38N
-16N
-37N
-57N
-21N
-31N
-30N
-39N
-30N
-43N
-18N
-27N
-28N
o
2
343
352
334
4
356
345
9
336
340
353
341
346
10
347
8
5
5
358
349
343
333
10
344
358
344
6
345
325
1
351
352
343
352
339
4
355
354
WA
a
b
m/o m/o
339
319
328
311
340
332
322
345
313
316
329
317
322
346
323
344
341
342
335
326
319
309
346
321
334
321
342
321
302
337
328
328
319
328
316
340
331
330
+1.0
+1.0
+1.1
+0.9
+9.9
+1.1
+1.0
+9.9
+0.8
+1.1
+1.1
+1.1
+1.0
+9.9
+1.2
+9.9
+9.9
+9.9
+1.1
+1.2
+1.1
+1.0
+9.9
+1.2
+1.1
+1.2
+9.9
+1.1
+1.0
+1.1
+1.1
+1.1
+1.2
+1.0
+0.9
+9.9
+1.1
+1.1
-9.2
-4.2
-5.7
-3.2
+9.9
-6.6
-4.5
+9.9
-3.4
-3.9
-5.9
-4.0
-4.6
+9.9
-4.8
+9.9
+9.9
+9.9
-7.5
-5.2
-4.3
-3.1
+9.9
-4.5
-7.4
-4.5
+9.9
-4.4
-2.6
-8.6
-5.5
-5.7
-4.3
-5.6
-3.7
+9.9
-6.4
-6.2
Si observa recuerde sincronizar su reloj con la Hora Legal de Venezuela, y al hacer su reporte restar 4h 30m. Su
observación es muy útil para los astrómetras.
Envíe su observación a: [email protected].
Es muy importante que tome los contactos: 1- Marte toca aparentemente el Disco Lunar; 2 – Marte se sumerge
detrás de la Luna, (desaparece); 3 – Marte aparece nuevamente emergiendo detrás de la Luna, y ; 4 – Marte se separa de
la Luna.
Es importante, si se observa en grupo, no copiar los datos de otra persona, cada observador debe reportar sus
propios datos y suministrar las características de su telescopio, tales como: Apertura del objetivo, Distancia Focal, Ocular
utilizado, tipo del telescopio, marca del telescopio, etc.
Para facilitar la recepción de datos, se sugiere enviar estos en grupo por Sociedad, asociación, o grupo
astronómico, y realizar esto en las 24 horas siguientes al evento.
Si fotografía envíe su foto en alta resolución en formato jpg.
Buena suerte y cielos despejados.
La Luz Solar puede bajar la presión sanguínea
La Hipertensión y las enfermedades cardiovasculares correlacionadas con la latitud y entrada al invierno.
Científicos han aprendido como la exposición a la Luz Solar reducen la presión sanguínea
University of Southaptom
Un
estudio realizado
en el Reino Unido
ha demostrado el
mecanismo por el
cual la exposición
a la luz solar
disminuye
la
presión sanguínea,
y reduce el riesgo
de sufrir un ataque
cardíaco.
El
estudio, publicado
en Enero 20 de
2014, en el Journal
of
Investigative
Dermatoligy,
muestra que la luz
solar logra esto en
el cuerpo humano
al
reducir
los
niveles de una
pequeña molécula
mensajera, Oxido de Nitrito (NO), en la piel y sangre.
El Oxido Nítrico, así como sus productos secundarios, abundantes en la piel, están relacionados con la
regulación de la presión cardíaca. Al exponernos a la luz solar, pequeñas cantidades de NO pasan de la piel a la sangre
bajando el tono de los vasos sanguíneos, y reduciendo la presión, lo que hace disminuir el riesgo de ataque cardíaco.
El conocimiento común muestra que la disminución a la exposición de la luz solar, disminuye el riesgo de sufrir
de cáncer de piel, pero no exponerse incrementa el riesgo de enfermedades cardíacas.
La incidencia de enfermedades cardíacas esta correlacionado con la latitud y el avance del invierno.
Esto es, Presión Arterial Alta e incremento en la incidencia de enfermedades cardiovasculares, se han observado
en invierno y en países alejados del Ecuador, donde la radiación UV del Sol es baja. Las enfermedades cardiovasculares
están asociadas a presión sanguínea alta, y causan el 30% de las muertes a nivel global cada año.
Durante un estudio, la piel de 24 individuos sanos fue expuesta a luz Ultra Violeta (UVA), en lámparas de
bronceado, en 2 sesiones de 20 minutos cada una. En una, los voluntarios fueron expuestos a los Rayos UV y al calor de
las lámparas, en la otra, los rayos UV fueron bloqueados y solo se les expuso al calor.
Los resultados sugieren que la exposición a los UVA dilata los vasos sanguíneos, reduciendo significativamente
la presión sanguínea, sin alterar los niveles metabólicos en la circulación, sin cambiar los niveles de vitamina D. Otros
estudios indican que los Óxidos de Nitrito preformados que quedan en la piel, mantienen estos efectos. Los datos fueron
consistentes con las variaciones estacionales de la presión sanguínea y riesgo cardiovascular a latitudes medias.
Estos resultados son significativos en los futuros debates acerca de los potenciales beneficios para la salud de la
exposición a la Luz Solar, y el rol de la Vitamina D en el proceso. Puede ser el momento oportuno para discutir los
riesgos y beneficios de de luz solar para la salud, y revisar las advertencias que se hacen al público. Quitando la
exposición excesiva a la luz solar, lo cual es crítico para prevenir el Cáncer de Piel, el miedo a hacerlo por miedo a esto, o
debido a ciertos estilos de vida que evitan la exposición al Sol, pueden causar enfermedades cardiovasculares. Tal vez con
excepción de la salud ósea, los efectos de tomar vitamina D, han sido desechados.
Al parecer los NO de la piel son muy importantes contribuidores a la salud Cardiovascular. En estudios futuros
se buscará más datos críticos, así como descubrir estrategias nutricionales, a fin de maximizar el almacenamiento de
Óxidos de Nitrito en la piel, y como llevarlos al sistema sanguíneo más eficientemente.
El Niño 2014. ¿Qué es El Niño de todos modos?
NASA
El Niño es un fenómeno que se produce a veces en el Océano Pacífico, pero como es tan grande afecta al clima
en el mundo entero.
El clima depende bastante de la temperatura de los océanos. Donde el océano está tibio, se forman más nubes y
cae más lluvia en esa región del mundo. En el
Océano Pacífico, cerca del ecuador, el Sol
hace que el agua en la superficie sea
especialmente tibia.
Normalmente los fuertes vientos del
ecuador empujan el agua tibia de la superficie
cerca de Sudamérica al oeste hacia Indonesia.
Cuando esto sucede, el agua más fría inferior
sube a la superficie del océano cerca de
Sudamérica.
Sin embargo, en el otoño y el
invierno de 1997-1998, estos vientos fueron
mucho más débiles que lo normal. Incluso, en
octubre, soplaron en la dirección contraria
(hacia Sudamérica en vez de hacia Indonesia).
Debido a esto el agua superficial tibia del
ecuador se acumuló en la costa sudamericana
(alrededor de Perú) y luego se trasladó al norte hacia California y al sur hacia Chile.
Muchos peces que vivían en las aguas normalmente más frías de la costa de Perú se alejaron o se murieron. Los
pescadores llaman a este fenómeno de aguas
costeras tibias y mala pesca "El Niño", en
alusión al "Niño Cristo," ya que en los años en
que se produce este fenómeno, aparece en la
época de Navidad.
En 1997 y 1998, se formaron muchas
nubes de lluvia sobre esta parte tibia del
océano. Estas nubes se trasladaron tierra
adentro y produjeron mucho más lluvia que lo
normal en Sudamérica, Centroamérica y los
Estados Unidos. Mientras que en otras partes
del mundo hubo sequía. En todo el mundo
hubo patrones climatológicos poco usuales,
creando lagos en desiertos y montones de
carbón en selvas tropicales.
¿Cómo podemos saber qué le pasa a
las temperaturas de los océanos en la Tierra? ¡La mejor forma es subir al espacio!
¿Cómo tomar la temperatura de los océanos desde el espacio?
Donde el océano es más tibio, el nivel del mar es levemente
superior. En 2008, el
satélite
Jason-2
(también llamada la
superficie del océano
Topography Mission)
fue puesto en órbita
alrededor de la Tierra.
Se continuó con las
mediciones que se
realizan por Jason-1,
lanzado
en
2001.
Ambos satélites tienen
una sensibilidad a
bordo del altímetro. Un altímetro mide la altura de sí misma hacia la superficie de la Tierra (tierra o agua).
Jason-1 utiliza el radar para medir las pequeñas colinas y valles de la
superficie del océano. Esta información ayuda a los científicos a comprender la
circulación oceánica y predecir los fenómenos climáticos como El Niño. Jason-1
fue lanzado en 2001 y todavía
está trabajando!
Jason-2,
también
llamada la superficie del océano
Topography Mission, continúa el
trabajo iniciado por Jason-1.
Jason-2 fue lanzado en 2008 y
todavía está en órbita y la
recogida de datos.
Con la información del
TOPEX/Poseidón, se pueden
crear mapas topográficos de las partes más altas y más bajas de la
superficie del océano. En los mapas planos, se usan distintos colores para
indicar las diferentes alturas del océano.
En estos mapas, los colores
violeta, azul y verde indican las partes
más frías del océano donde el nivel del
mar es un poco menor. Los colores rojo,
rosado y blanco son las partes más tibias
donde la superficie del océano sobresale
un poco. La superficie del agua donde el
océano es más tibio es sólo unos 2
metros (un poco menos de 7 pies) más
alta que en las áreas más frías.
Mientras preparas tu budín de
El Niño, piensa en el satélite Jason-1 y
Jason-2. Es como una furgoneta llena de
instrumentos en el espacio. Viaja
alrededor del mundo 4.700 veces al año
trazando mapas de la superficie del mar.
Jason-1 y Jason-2 son dos de varios
satélites que mantienen un ojo en
nuestros océanos y añadir a la
información que obtenemos de los
buques y boyas.
Aguas cálidas
se están moviendo
desde
el
Pacífico
Occidental
hacia
Suramérica con un
patrón más fuerte que el
de 1997 – 1998, El
Niño
más
intenso
registrado en el siglo
XX.
El evento se
espera
comience
a
desarrollarse en Julio y
pudiera
ser
muy
intenso.
Capa de Hielo Oeste de la Antártida
Según 2 estudios realizados en los glaciares del Oeste de la Antártida, el Colapso de la cubierta de hielo luce
inevitable, un evento que podría levantar el nivel de los océanos más de 1 metro. El primer estudio liderado por Eric
Rignot del JPL, se realizó utilizando satélites de NASA y observaciones desde aviones, el segundo fue liderado por Ian
Joughin, de la Universidad de Washington, y utilizó un modelo de computadora para comparar observaciones de
derretimiento reciente, con escenarios de derretimientos proyectados, para ver cual encajaba mejor. Ambos estudios
concluyeron que el segmento de hielo del Mar de Admunsen comenzó un declive irreversible que terminara con la
pérdida total de hielo, posiblemente en unos pocos cientos de años.
La región del Mar de Admunsen contiene varios glaciares de rápido movimiento, los que incluyen a Pine Island,
Haynes, Pope, Smith, y Kohler. Muchos glaciares antárticos poseen plataformas que funcionan como represas, pero no
hay casi nada en esta región, por lo que los glaciares fluyen libremente y estos glaciares drenan un tercio del hielo de la
cubierta de hielo Oeste de la Antártida.
En otro estudio publicado en Marzo de 2014 por Ringot, Mouginot, y Scheuchl se demostró que estos glaciares
se han acelerado, (Ver foto). Estas medidas entre 1996 y 2008 se muestran como Rojas donde se aceleró la perdida de
hielo y en Azul donde se frenó. La mayoría de los glaciares se han acelerado y los cambios se observan incluso tierra
adentro.
Un trabajo más reciente de Rignot examina en Mayo de 2014, el por qué estos glaciares se están acelerando, esto
lo hizo analizando observaciones satelitales. Observó que esta región se ha retirado significativamente entre 1992 y 2011.
Por ejemplo: El Glaciar de Pine Island se ha retraído 31 km tierra adentro; el Smith/Kohler 35 Km; Thwaites 14 km; y
Haynes 10 Km. Esto sugiere más declive en el futuro. La mayor parte del derretimiento viene de abajo. Las corrientes
oceánicas calidad derriten el hielo y le permiten fluir más rápidamente al volverse más fino el hielo y haciendo retroceder
el frente del glaciar.
Los glaciares del Mar de Admunsen han entrado en este círculo vicioso, y al parecer nada lo detendrá. La tierra
debajo de los glaciares en esta zona están debajo del mar, el agua que sale de los glaciares entra directamente a mar, no
hay topografía que frene el agua. Estas tres cosas: El derretimiento acelerado; el retroceso de los frentes de glaciar; y falta
de topografía que frene la salida de agua de los glaciares, apuntan a un colapso de la Capa de Hielo del Oeste Antártico.
Este escenario es igual en los estudios de Joughin, el cual dice que este colapso podría ser total en 100 o 200 años como
máximo. Este segmento posee agua suficiente para elevar el nivel marino en 1,2 m.
OPTICAL RESPONSE OF THE ATMOSPHERE DURING THE CARIBBEAN TOTAL
SOLAR ECLIPSES OF 26 FEBRUARY 1998 AND OF 3 FEBRUARY 1916 AT FALCÓN
STATE, VENEZUELA
MARCOS A. PEÑALOZA-MURILLO_
University of Essex, Environmental Research Laboratory, Central Campus. Wivenhoe Park,
Colchester, Essex CO4 3SQ, UK and Universidad de Los Andes, Facultad de Ciencias, Equipo
Interdisciplinario e Interdepartamental de Investigación Atmosférica Mérida, Edo. Mérida.
Venezuela
Abstract. An investigation of the optical response of the atmosphere before, during, and after the total solar eclipse of 26 February
1998 at the Caribbean Peninsula of Paraguaná (Falcón State) in Venezuela, was made by measuring Photometrically the intensity of the
sky brightness in three strategic directions: zenith, horizon anti-parallel or opposite the umbra path, and horizon perpendicular to this
path. From these measurements, and by applying in an inverse way an empirical photometric model, very rough estimations of the
extinction coefficient, and also of the average optical depth,
were obtained in one of these particular directions. However based on meteorological measurements such as those of relative humidity
and temperature, and applying a different model, a better estimation in the visual of the total global extinction coefficient of the sky
(except the horizon), were made considering the contribution of each component: Atmospheric aerosol, water vapour, ozone, and
Rayleigh scattering. It is shown that this global coefficient is mostly dependent upon aerosol extinction. In spite of the strong reduction
of sky brightness photometrically observed during the
totality, the results show that the sky was not dark. This is confirmed by the results obtained for the total global extinction coefficient.
Additionally it is estimated that the total solar eclipse that took place also in Falcón State, Venezuela, at the
beginning of the last century on 3 February 1916, was ∼30% darker that the 1998 eclipse, and that atmospheric aerosol played a
relevant and similar role in the scattering of sunlight during the totality as it was for 1998’s. Visual observations made during each
event, which show that at length only one or two bright stars could be seen in the sky, support the results obtained for both eclipses.
Keywords: Atmospheric aerosol influence, meteorological measurements, photometric measurements, sky brightness, solar eclipse,
tropic
1. Introduction
On Thursday 26th February 1998 the last total solar eclipse for Latin America of the past century and
millennium, and the eclipse No. 51 (out of 73) in the Saros Series 130 of solar eclipses, took place. In Particular it was
seen from northern South America, some Caribbean islands (Kuiper and van der Woude, 1998), and some Pacific islands
near the Latin-American west coast (for a general description _ Permanent affiliation: E-mail: [email protected]
Earth, Moon and Planets 91: 125–159, 2002. © 2003 Kluwer Academic Publishers. Printed in the Netherlands.
and coverage, see New Scientist, April 1998, Sky & Telescope, May 1998, and Journal of the British Astronomical
Association, June 1998). Venezuela was one of three continental countries where this eclipse could be observed (Figure
1) and, in fact, it was the fourth time during that century that the Moon shadow cone swept or touched Venezuelan
territory. The first one was on 3 February 1916, the second one was on 1 October 1940 (USNO, 1939), and the third one
on 12 October 1977 (Fiala, 1976). These last two, unfortunately, either passed over a very remote región in the jungle
(southern Amazonas state) which at that time was almost uninhabited and hard to reach, or occurred when the eclipsed
Sun was already at the sunset (at Puerto Ayacucho, Amazonas State capital), respectively. Neglecting these two, the first
one and the most recent one have been the total solar eclipses that have draw the attention of Venezuelan people, mainly,
because one was at the end of the morning (1916) and the other during the first half of the afternoon (1998) both covering
well-populated regions of the country (Ugueto, 1916; Espenak and Anderson, 1996). Ugueto (1916) and del Castillo et al.
(1916) published reports in which they account for some astronomical, atmospheric and meteorological observations for
the eclipse of 1916. Other reports, such as those by Sifontes (1920), Röhl (1932) and Peñaloza (1975), however, account
only for meteorological or astronomical observations in three of the solar partial eclipses which took place in Venezuela
in the twentieth century many times. Thus eighty-two years had to elapse from 1916 until a new opportunity arrived for
observing a total eclipse of the Sun from Venezuela. The present research focused on carrying out photometric
observations of the visual sky brightness at the zenith and on the horizon during the total solar eclipse on 26 February
1998 at the Caribbean Peninsula of Paraguaná (Figure 2).
This is located in the northern part of the north-west Venezuelan State of Falcón. Ignoring the light of the solar
corona and air-glow, the visual sky brightness during a total solar eclipse is produced in part by atmospheric aerosol
particles which at least scatter light taking place within the penumbra (first order scattering) and scatter light taking place
within the umbra (second order scattering) as a consequence of a first order scattering within the penumbra, as depicted in
Figure 3 (Zirker, 1995). Therefore the ambient or environmental conditions of the air of a particular area or region
determine the local conditions by which the visual sky brightness is produced and thereby observed during a total solar
eclipse. The sky could be darker or brighter depending on the air quality during the totality around the observation zone.
It is interesting to note that reports of darkness during total solar eclipses in the ninetieth century indicate that they were
darker than those of the twentieth century (Silverman andMullen, 1974). This is, of course, circumstantial since it
depends on the local air quality of the observation site which, in turn, depends on the variability of atmospheric pollution.
Today pollution is stronger and potentially can contribute to make less dark the sky during a total solar eclipse when it is
being observed from urban or industrial areas.
It is interesting to highlight that before 1944 it was believed that the general brightness of the sky during the full
phase of a total solar eclipse was due to the brightness of the solar corona. It was not until Betenska (1944)
definitely
OPTICAL RESPONSE OF THE ATMOSPHERE DURING SOLAR ECLIPSES 127
Figure 1. The eclipse path through northern South America and the Caribbean. The shadow passed
overMaracaibo city, the biggest one along the path and the second biggest one of Venezuela (Espenak
and Anderson, 1996).
confirmed that the part played by the light of the solar corona in the general brightness of the sky and the illumination of
the landscape is insignificant and that this brightness is related to the light coming from the surrounding atmosphere and
which penetrates into the shadow. However an early account given by Lockyer (1927) on the total solar of eclipse of 29
June 1927 in England (Marriot, 1999) showed that the light emitted by the corona was evidently not very great because
this observer could not record any perceptible shadow being cast by it on a white sheet, in spite of the fact that the corona
was exceedingly bright (on this point, see The Illumination Engineer, July 1928, p. 128). This lead to the idea that the
illumination during totality is due mainly to diffused daylight by the atmosphere. Although the sky brightness is
dependent not only on the particular direction of sight but also on the solar elevation during a solar eclipse (Schaefer,
1993), as on a normal day, the photometric observations were made in the zenith and in the horizon. The closer toward
the zenith is looked at, the larger is the proportion of multiply-scattered light observed. Looking towards the horizon the
scattered light will include a proportion that is singly scattered. The zenith has been the sky point most photometrically
observed during the occurrence of a total solar eclipse (Silverman and Mullen, 1974). Since Halley (1715) made the first
report of his solar eclipse visual observations, it also has been thoroughly reported by The Photometric results presented
in the first part of this paper are observational and no theoretical evaluation is made. Potential theoretical interpretation of
them (or of future eclipses) could be attempted considering the approximate models published by Gedzelman (1975), and
Shaw (1978), respectively. Unfortunately the equipment used in this work did not allow for measurements depending on
a specific wavelength.
Figure 2. Clear picture of the head-shaped Peninsula of Paraguan´a from space taken by the KIDSAT camera on board
the space shuttle. This peninsula is a semi-arid zone connected to mainland through a very narrow strip of land called the
Isthmus of the Medanos (seen in the picture like a “neck”). The Gulf of Venezuela is to the left (photo courtesy of
NASA).
Figure 3. During a total solar eclipse multiple scattering in the Earth’s atmosphere can take place.
An instrument in the umbral shadow measuring towards the zenith receives sunlight that has been
scattered twice as in (a); towards the horizon, the instrument measures sunlight scattered once as in
(b) (adapted from Zirker, 1995).
an appreciable number of observers that it is on the horizon that major dramatic changes in brightness and colour take
place during a total solar eclipse.
In addition it is necessary to take into account the particular characteristics of each eclipse observation site
(surface albedo, geometrical and terrain factors, environmental measurements related to atmospheric aerosol
characterisation, etc.), and also the characteristic of the measurements made (wavelength, instrumentation, region of the
sky measured, etc).
By applying, empirical models given by Schaefer (1993), results derived from these photometric easurements
and those made by others of meteorological parameters, such as relative humidity and temperature, during the whole
eclipse, are presented for the extinction coefficient. Based on these results an estimation of the sky darkness or brightness
degree during the totality of the 1998 eclipse is made for the observation site onsidering the contribution of each
atmospheric component, namely, atmospheric aerosol, water vapour, ozone, and ayleigh scattering.
Using the meteorological data published by Ugueto (1916) for the 1916 total solar eclipse, additional results were
obtained and a comparison between these two eclipses could be made. The paper closes with a summary of the results
obtained and conclusions.
2. Local Circumstances of the Eclipse Observation Site
For Venezuela the eclipse covered the north–western part of the country, including Maracaibo, the second
Biggest Venezuelan city. Then, the Moon shadow swept, in a south–west to north–east direction, the Gulf of Venezuela
passing next over the Paraguaná Peninsula (Espenak and Anderson, 1996) where the observation site for this project was
chosen. In particular, this site was located in a semi-remote and semi-arid flat area in the northern part of the Peninsula
called Punta de Barco, at 69◦55_54__ W, 12◦09_52.8__ N, and 0 m above sea level, as reported by ARVAL amateur
team (from Caracas, and hereafter referred to simply as the Arval Observatory), where the central line of the totality
crossed through (Figure 4). The former installations of the booster station of “La Voz de Venezuela” Radio at this place,
near the beach, served as a camp and to set up the equipment. For this place the eclipse astronomical circumstances were:
first contact at 12:38:20, second contact at 14:09:18, midtotality at 14:11:10, third contact at 14:13:02, fourth contact at
15:35:43, all these times are given in local time (UT-4). The Sun altitudes were 69◦ for the 1st contact, 62◦ for the
mideclipse, and 45◦ for the 4th contact. The totality lasted 3 min 44 s (Arval Observatory). To the unaided eye the
atmospheric conditions for the day of the eclipse were in general good and acceptable. However some cloudiness near the
horizon was reported by the ARVAL Observatory around the observation site being the maximum of 5/8 at 10:30 am and
the minimum of 1/8 between 12:30 pm and 5:00 pm. A variation of approximately −5 ◦C in temperatura was noted
between 12:42 and 14:12 (local time) due to the eclipse. Figure 5 displays a sequence of six satellite images taken on 26th
February 1998 of western Venezuela by the NASA satellite GOES-10, including Paraguaná Peninsula, showing the
cloudiness variation at different times over this region. Note that at 11:08:00 am, local time, there were some clouds
around the zenith of the observation site (Figure 5a). Later on the 1/8 cloudiness referred to above was located to the
north of the Peninsula over the sea (Figures 5b–f), and the zone remained practically with clear sky. In particular Figure
5c shows the shadow falling to the west before crossing the peninsular area (at 01:44:00 pm local time), and Figure 5d
shows the shadow crossing it (at 02:08:00 pm local time). The penumbra is also seen in these pictures. Anderson (1999)
analysing two of the GOES images, describes the general pattern cloudiness and its processes originated in this region, as
well as in the northern part of the country, due to this crossing.
3. Instrumentation and Experimental Procedure
The photometric measurements were made by means of three different photosensors:
one photosensor was a Macam detector, model SD10Q-Cos (No. 1738), 15 mm2 area, hemispherical field-of-view
(∼180◦), covering wavelengths from 400 nm to 700 nm and with a maximum spectral response at 560 nm; the second
was an RS (stock no. 308-067), 5 mm2 area, 17.1◦ field-of-view, covering wavelengths
from 300–1200 nm, and a maximum spectral response at 900 nm; and a third one was an Ealing Electro-Optics (EEO)
Broad Band Silicon Detector, 0.38 cm2 area, hemispherical field-of-view (∼180◦), in combination with a photopic filter
(400–700 nm), both used with an EEO Research Radiometer/Photometer unit.
Figure 4. Map of the Paraguan´a Peninsula showing the central line of the shadow (green line) crossing
it. This line entered at Punta Jacuque and left the Peninsula at Punta de Barco (just in the top to the
right) where the observations were made (map courtesy of ARVAL Observatory).
Figure 5. Sequence of six satellite images taken on 26th February 1998 of western Venezuela by the NASA satellite
GOES-10, including Paraguan´a Peninsula, showing the cloudiness variation at different times. The zone remained
practically with clear sky. In (c) the shadow is seen falling to the west before crossing the peninsular area, and in (d) the
shadow is crossing it. The penumbra is also seen in these pictures (images courtesy of NASA).
The photosensors were calibrated at Essex University before they were taken to Venezuela (Peñaloza, 1999). To
perform this, a Wotan Xenophot HLX quartz diffuser bulb, with a tungsten filament, was used as a light source, and to
compare, a LI-COR integrating quantum/radiometer/photometer, model LI-188B was also used. Different glass neutral
density filters were applied in the calibration procedure in order to obtain the respective calibration curves in
kilorayleighs (kR). All photosensors during calibration were illuminated totally to account for the wide field-of-view of
two of them.
The rayleigh, a photometric unit introduced by Hunten et al. (1956) for the airglow and aurora, has been almost
niversally adopted by experimentalists in aeronomy (Baker and Romick, 1976). Also it has been adopted in contemporary
works dealing with the sky brightness during solar eclipses (Sharp et al., 1966; Dandekar, 1968; Velasquez, 1971;
Dandekar and Turtle, 1971; Lloyd and Silverman, 1971; Miller and Fastie, 1972; Carman et al., 1981). Historically, the
rayleigh unit was defined as an emission rate of 1 million photons per second from an extended column of 1-cm cross
(Baker and Romick, 1976). In SI units this is equal to 1010 photons s−1 m−2 per column. As stated by Baker (1974) the
justification to use a radiance (or surface brightness) unit like this relies on the fact that in gaseous photophysics the
photon is conveniently treated statistically along with the concentration of the other particles of the medium; this unit
gives a measure of the rate at which photons coming down from a region of the sky would strike each square centimetre
of normal area per time unit, and the word “column” is inserted to convey the idea of an emission-rate from a column of
unspecified length. The factor to convert photons per second into watts of light energy is simply hc/λ times the photon
rate, where the constants have their usual meanings and λ is the wavelength. For a full appreciation of this unit and further
details, the reader is referred to the works by Baker (1974), and Baker and Romick (1976).
In the in situ experimental procedure, and by applying the corresponding eclipse map given by Espenak and
Anderson (1996), an arrangement of the three photosensors was set up so that the Macam’s, covered with a white diffuser
size of 64 mm2, pointed to the horizon, perpendicular to the totality path (altitude 0◦, azimuth 150◦); the EEO’s also to
the horizon but anti-parallel to the totality path (altitude 0◦, azimuth 240◦); the RS’s, covered with a white flashed opal
glass diffuser of 25 mm diameter, to the zenith. This direction determined that this photosensor (device diameter, 8.26
mm) was housed in a cylindrical black case, 57.88-mm height and 25.66-mm width (for a narrow field-of-view of 17.1◦).
Previous technical checking against the horizon and zenith during a normal day (see below), and based on the fact that it
has been noted that in past total solar eclipses the horizon is brighter than the zenith, showed that the appropriate
distribution and setting of the photosensors was that referred to above. Because the horizon detectors have wide field-ofview it was not necessary to measure exactly their altitude within a degree precision.
Otherwise, with small field-of-view detectors, the exact altitude of the instrument should be stated to the nearest
degree since a precise knowledge of this parameter is vital for any comparison with models; the sky brightness vary
greatly with even the change of one degree in altitude near the horizon.
The arrangement was installed in the roof of the booster radio station wáter tank supply, high enough over the
ground to have a good view all over the horizon. The photosensors were directed inland, opposite the sea. In this way the
predominant surface albedo was that corresponding to a semi-desertic ground. Buildings belonging to the booster station
and other obstacles in different lines of sight to the sea prevented the horizon photosensors from pointing in those
directions. The zenith distance of the Sun during the eclipse was quite enough apart so that it was not necessary to screen
it in order to carry out the zenith measurements. Due to the light colour of the water tank roof’s surface, care was taken to
put the photosensor arrangement just on one edge of the roof in order to avoid possible interference of the
shadow bands which were abundant after the third contact according to unaided eye observations made on this
surface.
4. Observations
The output signal measurements from the sensors were simultaneously acquired with a data-logger, at a rate of
one eading per minute per channel for six hours (from 11:00 am to 5:00 pm), to cover part of day light under normal or
noneclipse conditions for reference purposes. The resolution value of 1 μA corresponding to the channel used to acquire
the current signal from the Macam sensor, prevented from measuring signals below this quantity.
Therefore minimum values related to these measurements during the totality, which were below this limit, had
to be interpolated by using the second and third contact values, respectively. Figure 6 shows the profile of the horizon sky
brightness perpendicular to the shadow path obtained with the Macam sensor, in the wavelength range of 400–700
nm, from 11:00 am to 5:00 pm Venezuelan local time. As can be seen the stability of the device was very good as it was
for the other instruments. This brightness is presented along the ordinate on a logarithmic scale in the unit of kR, and the
minimum value obtained during the totality was approximately 6 × 102 kR. The horizon sky brightness profile obtained
with the EEO detector in the direction of the shadow path but opposed to it (anti-parallel) are shown in Figure 7. As in
Figure 6, this brightness is presented on a logarithmic scale in kR. Between 13:38 and 14:35 this sensor caught some
significant spurious or extraneous signals of unknown origin (some of which, in turn, were also detected by the Macam
sensor in a lesser magnitude and removed from the raw data) whose origin or source could not be identified. James (1998)
measuring the zenith sky brightness at the same location (Punta de Barco) with a portable luxmeter but with
hemispherical view also obtained some offset points during the totality. These spurious signals also OPTICAL RESPONSE OF
THE ATMOSPHERE DURING SOLAR ECLIPSES 135
Figure 6. Plot showing the horizon sky brightness profile perpendicular to the shadow path obtained
with the Macam sensor, in the wavelength range of 400–700 nm, from 11:00 am to 5:00
pm Venezuelan local time.
Figure 7. Plot showing the horizon sky brightness profile obtained with the EEO detector in the direction
of the shadow path but opposed to it (anti-parallel), in the same wavelength range (photopic),
and in the same time period, as in Figure 6.
had to be removed from the raw data of this sensor. Yet in this case, however, by using the second and third contact
again, values corresponding to this period including those during the totality were extrapolated and interpolated,
respectively. In this case the minimum value obtained for the totality was approximately 3×105 kR.
Figure 8 shows the profile corresponding to the zenith sky brightness in the same units, obtained with the RS
photosensor in the wavelength range of 300 – 1200 nm. During the totality the minimum value obtained for this celestial
point was approximately 2.7 × 10 kR.
Percent obscuration at the ground level is presented for the zenith curve at the top axis of Figure 9, for a period of about
16 min that includes second and third contacts
Figure 8. Profile of the zenith sky brightness obtained with the RS photosensor, with a narrow
field-of-view, the wavelength range of 300–1200 nm, and in the same time period in Figure 6.
.
5. Extinction Coefficient and Optical Depth Estimations
A direct estimation of the total extinction coefficient in the visual, kg [in mag/air mass (defined below)], towards
the zenith due to the contributing components, is given by:
kg = kR + ka + koz + kwv, (1)
where kR is the Rayleigh scattering component, koz is the ozone component, ka is the atmospheric aerosols component,
and kwv is the water vapour component. In general, for other directions it is more complicated, and the extinction
coefficient as defined by Schaefer (1993) should be taken into account. However, for all but low horizon observations, an
approximate usage of Equation (1) is adequate to describe the general state of the atmosphere because the air masses are
basically identical for all components when the horizon area is avoided. Hence kg will be called the global total extinction
coefficient. Then the components, given in Equation (1), according to Schaefer (1993, 1998), are:
kR = 113700(n − 1)2 exp[−H/He)]λ
−4, (2)
Figure 9. Zenith sky brightness as a function of the percent solar’s disk obscuration (top axis) by the Moon, at the ground
level, for a central period of 22 min around the total phase that includes the second and third contacts.
koz = (0.031/3.0){3.0 + 0.4[φ cos(αs) − cos(3φ)]}, (3)
ka = 0.12[0.55/λ]1.3[1 − (0.32/ ln S)]4/3[1 + 0.33 sin(αs)] exp(−H/1.5), (4)
kwv = 0.94WλS exp(t/15)exp(−H/8200). (5)
In Equations (2)–(5), n is the index of refraction at sea level, λ is the wavelength (in microns), H is the observer’s
height (in km) above sea level, He is the scale height (in km), φ is the observer’s latitude (in radians), αs is the right
ascension of the Sun, Wλ is a function of the wavelength, t the air temperature (in ◦C) and S is the relative humidity.
Equation (5) can be found in Schaefer (1998). A stellar magnitude, mag, is a logarithmic unit of intensity, where one
magnitude corresponds to roughly a factor of 2.52 in brightness regardless in what units the intensity is given. This is the
basic unit of brightness used by astronomers; if I is an intensity, the magnitude is defined by the expression C−2.52 log10
I, where C is an arbitrary constant (Young, 1990; Hearnshaw, 1992). In general, on the other hand, the unit of
atmospheric distance is given by the local relative optical path length, which is defined as the ratio of the optical path
length along any trajectory to the vertical path length in the zenith direction (one air mass). Therefore the units of
astronomical extinction are magnitudes per air mass (mag/air mass); one magnitude per air mass equals 2.52
log10e (∼= 1.086) optical depths per air mass (Taylor et al., 1977; Bruin, 1981) (see Equation (13) below).
It is well known that atmospheric aerosols come from many sources (sea spray, windborne desert dust, etc.).
Fortunately there are a variety of trends which can be used to provide a reasonable guess for the aerosol extinction
coefficient, ka. Thus Equation (4) is based on an evaluation of trends for time of the year, relative humidity, altitude, and
wavelength. Additional sources of extinction such as volcanic aerosol layers and urban pollution, not included in this
analysis, have to be treated, respectively, in a different and appropriate manner. Schaefer (1993) states that the use of the
equations above allow for the extinction to be reasonably estimated for any site in the world provided that urban areas and
special situation of volcanic events are not included._ Therefore for application purposes of this model, it must be
stressed that only a remote or a semi-remote site has to be considered.
Therefore for Rayleigh scattering He = 8.2 km (Allen, 1973). For visual wavelengths (λ = 0.55 μm), and for
Punta de Barco site in particular, these equations are reduced to:
kR = 0.1066, (6)
koz = (0.031/3.0){3.0 + 0.4[0.21 cos(αs) − 0.80]}, (7)
ka = 0.12[1 − (0.32/ ln S)]4/3[1 + 0.33 sin(αs)], (8)
kwv = 0.029S exp(t/15). (9)
By applying Equation (1), taking into account Equations (6)–(9), kg can be found for the atmosphere of this
articular ocation during the day of the eclipse. To find αs calculations with the AstroScript software provided by DuffetSmith (1997) were performed. The values for S and t were taken from the data published in the ARVAL Observatory web
site, whose team was in the same location making meteorological observations. Figure 10 displays the variation of the
relative humidity (in %) on 25/02/98, from 07:30:00 to 17:30:00 (local time), and on 26/02/98, from 09:30:00 to 17:30:00
(local time), and Figure 11 displays the same variable during the whole eclipse, from 12:42:00 to 15:39:00 (local time).
Figure 12 presents the temperature measurements made the day of the eclipse also by the ARVAL Observatory.
_ Indeed the aerosol density can vary by large factors. But the bulk of the variance arises due to effects of altitude,
relative humidity, and time of year. Equation (4) incorporates these effects by giving the equations for the best correlation
between the quantities involved. When these correlations are accounted for, a large fraction of the variance in the
“standardized” aerosol density (i.e., standardized to sea level, zero relative humidity, temperate northern latitudes, and
near the equinoxes) is eliminated. Even so, there can still be large variations around the best value of the specific
equations involved due to manmade pollution, forest fire, volcanoes, etc. Nevertheless, from a very large data base with
>105 measurements from >300 sites worldwide, the scatter of Equation (4) is remarkably good (B. Schaeffer, personal
communication, 1999).
Figure 10. Variation of relative humidity the day before (25/02/98), from 07:30 to 17:30 (local time),
and the day of the eclipse (26/02/98), from 09:30 to 17:30 (local time), measured by the ARVAL
Observatory at Punta de Barco (Paraguan´a Peninsula, Falc´on, Venezuela).
Figure 11. Variation of the same variable as in Figure 10 but during the whole eclipse, from 12:42 to
15:39 (local time), measured by the ARVAL Observatory at the same location as in Figure 10.
Figure 12. Variation of temperature during the eclipse between 12:42 and 15:39 (local time),
measured by the ARVAL Observatory at Punta de Barco (Paraguan´a Peninsula, Falc´on, Venezuela).
It is important to note that the primary analysis of this paper is not to calculate, in a particular direction, the
extinction coefficient, k, via photometric measurements of the sky brightness by applying Equation (13). However, they
can in principle be useful to explore this possibility in the way described next.
Being the horizon direction unacceptable for the aforementioned model, the photometric measurements made of
the horizon sky brightness under noneclipse and eclipse conditions could be used to estimate, in a rough way, the
extinction of the atmosphere (and its corresponding optical depth) in this particular direction along that day, using a
photometric model presented by Schaefer (1993). By experience it is well known that these parameters can vary quite
widely with altitude and azimuth as well as from hour to hour, from minute to minute, and so on, within a given day. So
the best that can be done is to use an average value to represent the sky conditions for a given date and direction.
Ideally, the sky brightness should be calculated taking into account multiple scattering. However in a first approximation,
according to Schaefer (1993), a semiquantitative estimation of the cloudless sky brightness in nanolamberts (nL) during
daylight can be given to 20% accuracy by,
Bday = Nλf (ρsun)10−0.4kX(Zsun)[1 − 10−0.4kX(Z)], (10)
where k is the total extinction coefficient, defined here in units of stellar magnitudes per air mass; Zsun and Z are the
zenith distance of the Sun, and the sky direction, respectively; ρsun is the separation between the sky direction and the
Sun; X(Zsun) and X(Z) are the respective air mass functions; Nλ is a coefficient depending on wavelength λ (for the visual
it is equal to 11,700); and f (ρsun) is an approximate scattering phase function given by Krisciunas and Schaefer (1991),
f (ρsun) = 105.36[1.06 + cos2 ρsun] + 106.15−(ρsun/40degree)
+6.2 × 107(ρsun)
−2, (11)
with ρsun measured in degree. This function gives values much too high for small values of ρsun. Schaefer (private
communication 1999) suggests that for ρsun < 20_ it should be replaced by a different expression (note that the angular
diameter of the Sun is about ∼ 32_ at mean Earth distance so in fact for ρsun < 15_ the Sun is being looked at). Therefore
for the purpose of the present work, in which values of ρsun _ 15_ are involved, the use of Equation (11) is sufficiently
valid. For altitudes near the horizon, but not below,
X(Z) = [cos Z + 0.025 exp(−11 cos Z)]−1, (12)
is a convenient and a fairly good approximation for reasonable elevations above sea level and aerosol density (Rozenberg,
1966).
Given the values of Bday obtained from the photometric measurements, and by solving numerically Equation
(10), approximate values of k were found for different values of the other parameters calculated from Equations (11)–
(12). Then the results can be used to estimate the optical depth (in any direction Z) for different
values of k by applying,
k = 1.086τ, (13)
where k is given in mag/air mass, and τ is the optical depth (Schaefer, 1993); this optical depth depends, in a proportional
manner, on the geometrical path, air density, characteristics of components, and sec Z. By comparison, the difference
between the extinction coefficient given by Equation (1) and that given by Equation (13), can be distinguished.
Although Equation (10) is transcendental for k, it could be solved for most of the input data by applying a
omputer code. To find values of Zsun the AstroScript software by Duffet-Smith (1997) was used. Because the angle ρsun
was available only for the horizon anti-parallel direction (opposite the shadow path), the calculation of k was only
possible for that particular direction. Zenith direction was not considered since during total solar eclipses, second order
scattering plays an important role in the zenith sky brightness (Figure 3). Although in Equation (10) the two terms
involving powers of ten account for not only the case of single scattered light but also for double scattered light, the term
representing the phase function [Equation (11)] only account for single scattering; therefore, Equation (10) cannot
be applied to the zenith direction.
Note that Equation (10), through the factor Nλ, is wavelength-dependent. Thus an integral over the spectral
responsivity of the detector must be made. Also this equation is dependent on direction; using a wide field-of-view
detector an integration over sky position in the field of view must be made. Finally, it is emphasised that the changing sky
brightness during the totality is primarily due to varying fractions of atmospheric illumination within the penumbra;
therefore, any comparison can only be correctly made with a detailed model involving the multiple scattering of light and
the geometry of the specific eclipse. However by taking into account that the photometric measurements made with the
EEO’s sensor were integrated in the visual range (400–700 nm ), a value of 11,700 for Nλ is given for this range
(Schaefer, 1993). By its wide field-of-view, the detector considered (EEO) also integrates in a hemispherical way the
light over the sky position. However considering that the sky brightness decreases from the horizon to higher altitudes
(except in that area close to the Sun) (Jeske, 1988), and that the sensor collects the light on the horizon between 0◦ and
180◦ on this plane but in altitude only between 0◦ and 90◦, the light mostly comes from the horizon. Thirdly, a single
scattering process in the penumbra produces much of this light. In this manner, the values of Bday to be used in Equation
(10) are instrumentally integrated and the corresponding values of k can potentially be interpreted as a rough estimate of
this parameter in that direction, in that spectral range. For qualitative purposes these values can be considered suffice to
outlook the variation of the extinction coefficient in the visual and in the specified direction. In the calculations a
conversion factor of 47.6 nL/kR was applied which was obtained from the data given in Table II of the paper by
Dandekar (1968). There it is stated that 0.9 mL is equivalent to 21.0 kR/Å; taking into account that the effective width of
the visual is ∼900 Å, 1 kR = 9 × 105 nL/(900 Å × 21 kR/Å) = 47.6 nL. As it is known, one lambert is equal to one lumen
(lm) per square centimetre and a lux (lx) is one lumen per square metre. The latter has recently been used by Shiozaki et
al. (1999), Darula and Kittler (2000), and Darula et al. (2001) in their papers related to variations of daylight during solar
eclipses. In other recent paper on sky brightness when the sun has been in eclipse at dawn, the candle per square metre
unit has been used by Liu and Zhou (1999). This demonstrates that photometric measurements and their units, in its
different forms, continue nowadays being used to study the sky brightness during solar eclipses since the first reliable
instrumental observations of this type were made in the last quarter of the ninetieth century by Abney and Thorpe (1889);
moreover, these are justified when they have to be associated to visual observations (as in this paper).
In order to have a conversion factor from any of these units of luminous flux to radiant flux (i.e., [lm W −1]), a quantity
called luminous efficiency of the radiation has to be defined which, in turn, depends on wavelength (Middleton, 1952).
For example, it has a value of 685 lm W−1 at 5550 Å (McCluney, 1968). The method to obtain the integrated
factor, as well as other conversion factors between radiometric-photometric units, implies an integration process over the
wavelength range of interest which takes into account this efficiency and the specific radiometric quantity involved. For
further details the reader is referred to Lovell (1953), Meyer-Arendt (1968) andMcCluney (1968) who give basic
comprehensive treatments on this matter.
6. Results, Discussion and Analysis
Due to the different sensors used and their variability in solar wavelength sensitivity span and spectral response,
a strict intercomparison among these curves is not possible. Nonetheless some useful information can be obtained. First
of all with the support of Figure 7, it can be estimated that the horizon sky brightness is reduced by about three orders of
magnitude as compared with that due to the uneclipsed Sun during the morning and also during the afternoon. Note that
the curve is not symmetric around the midtotality. Given the specific direction involved (perpendicular to the Sun track
vertical plane) this is a consistent feature because in normal conditions the horizon sky brightness had decreased steadily,
from the morning until late in the afternoon. The minimum value observed in this case during the totality was
approximately 7 × 10 kR (70 kR). For comparison note that the brightness of the night sky is about 250 R (0.250 kR) and
the aurora lies between 1 and 1000 kR (Jerrard and McNeill, 1986). Therefore the horizon sky brightness in this particular
direction, and during the totality, turned out to be ∼ 280 times brighter than that of the night sky, or alternatively, ∼ 36
times brighter than that of the typical sky at full Moon. The maximum value observed during the morning (pre-eclipse)
was
∼ 6.5 × 104 kR, and the maximum value during the afternoon (post-eclipse) was
∼ 2.2 × 104 kR which are values, in order of magnitude, near those typical of the
brightness for a normal day light clear sky (6.95 × 105 kR). This indicates that the horizon sky brightness in that
direction, and under noneclipse conditions, was 10 times less bright than that of a typical daytime. Taking the maximum
(noneclipse condition) and minimum (totality) values as references, the reduction in brightness was a factor of 103. This
kind of reduction has been observed by Dandekar and Turtle (1971) during the total solar eclipse on 7 March 1970, at
solar azimuth 180◦ and a distance 90◦ away from the Sun, at 630 nm wavelength.
From Figure 7, it could be estimated that the horizon sky brightness, opposite the umbra path, is reduced by only
one order of magnitude as compared with that due to the uneclipsed Sun during the morning and also the afternoon. It is
convenient to bear in mind that this is the direction containing the Sun track vertical plane. During the morning this
direction is opposed to the Sun, and during the afternoon it is approximately in the direction of the area just below the
Sun. The curve is not symmetrical around the midtotality but it is inverse to that of Figure
6. The sky brightness on a normal day increases from that particular direction as long as the Sun is going down
towards its sunset. The minimum value estimated during the totality was approximately 2.4×105 kR. The maximum
value observed during the morning (pre-eclipse) was ∼ 3×106 kR, and during the afternoon (posteclipse), ∼ 1.5×107 kR.
In comparing these two latter figures with that of a typical daytime sky, it is noticed that in this particular
direction the horizon was brighter than that of a typical daytime sky by a factor of 10 and 102, respectively. However this
last factor is possibly enhanced to this order of magnitude due to a significant contribution of the direct solar radiation
arriving at the detector, given the direction considered which is, during the afternoon, towards the sky area below the Sun.
From Figure 8, the zenith sky brightness has a reduction of about three orders of magnitude as compared with that due to
the uneclipsed Sun. This reduction is similar to that obtained for the horizon perpendicular to the shadow path. Recalling
that the Sun never was into the field-of-view of the RS detector (17.1◦/2 = 8.55◦), the maximum zenith sky brightness preand post-eclipse was ∼104 kR during the period covered, indicating that this brightness was constant throughout the
period covered for the uneclipsed Sun, that is to say, regardless of the position of the Sun. This is consistent with the
zenith sky brightness measurements made by Dandekar (1968), Velazques (1971), and Shaw (1975). For the totality, the
minimum value was ∼ 2.7 × 10 kR (27 kR) being approximately 108 times brighter than the night sky, or alternatively,
∼14 times brighter than that of the typical sky at full Moon.
This last result is quite consistent to that obtained by James (1998) who inferred that the zenith sky brightness at
the same location (Punta de Barco) was equivalent to ∼10 times the fullMoon sky brightness. Silverman andMullen
(1975) reviewing the sky brightness during eclipses consider many related possibilities as references; among them are:
photometric results, star sightings, twilights, comparison with moonlight, and visibility of printed or written letters,
instrument parts, and objects.
They state that an estimate of the brightness ten times that of a full Moon is, of course, considerably less than the true
value. Thus it is reasonable to think that the result obtained in this work is more reliable. Ignoring this discrepancy it can
be said that the zenith was somewhat brighter than a typical full-Moon-sky.
From this result quoted it can be noticed that the zenith brightness turned out to be less bright than the horizon which, in
turn, is a result consistent with those obtained in past total solar eclipses. In particular, it has been found that the horizon
Figure 13. Profile of the global total extinction coefficient in the visual and those for each component
contributing to it, between the first and fourth contacts, calculated from meteorological data provided
by the ARVAL Observatory and using an empirical model by Schaefer (1993), at Punta de Barco
(Paraguan´a Peninsula), Venezuela. Note that the total profile is controlled by the aerosol profile. The
water vapour profile is also included for comparison purposes.
perpendicular to the shadow path is approximately 2.6 times brighter than the zenith. This result is very similar to that
found by Schaefer (1986) who studied the brightness of the night sky (roughly twice) for a set of “standard” observing
conditions at Cerro Tololo Interamerican (Chile) and Kitt Peak National observatories.
From Figure 9 the brightness begins to change just 6 min preceding and following the totality. In terms of solar
obscuration, this change begins to occur when the solar disc has been obscured by 91.99%. In terms of solar brightness it
begins to appear when the sun magnitude has fallen by 3 units, approximately, few minutes before the onset of totality at
second contact (Hughes, 2000). Yet this change is even more drastic when this percentage yields 98.81% as can be seen
in this figure.
Below this value effects associated with total solar eclipses can be interpreted in terms of attenuated, but
otherwise essentially unchanged Sun (Sharp et al., 1971).
Figure 13 shows the profile of the global total extinction coefficient in the visual, kg, and those for each
component contributing to it, between 12:42 and 15:39 (local time), are also shown. It is evident that the aerosol is the
main contributor to this coefficient in comparison with the other two (water vapour, Rayleigh and ozone extinction) so
that ka _ kwv > kR > koz. It is also seen that it is strongly dependent on relative humidity (see Figure 11) which rises
during the totality and just after it (see Figures 10 and 11). This last feature is consistent with observations made of
relative humidity in past eclipses (Ugueto, 1916; Brooks et al., 1941; González, 1997). The calculation of kg in the way
shown by Equations (1), (6)–(9), is very useful because it gives an estimation of the general darkness of the sky during
the totality. Table I presents values for kg, for seven different situations at night, taken from Schaefer (1986). Note from
this table that a very poor night has a kg = 0.50 mag/air mass; from Figure 13 it can been seen that, for example, at 14:07
(local time) this coefficient increased to a value of 0.86 mag/air mass, and for 14:12 a value of 1.11 mag/air mass was
obtained, indicating a very poor “night” during the totality. In fact only Mercury, with an apparent visual magnitude (mV)
of −0.2, Jupiter (mV = −2.6) and Venus (mV = −4.22) were seen clearly close to the Sun by this author, and only two
stars, Deneb (α Cyg) with mV = 1.25 (Allen, 1973), and Fomalhaut (α PsA) with mV = 1.16 (Allen, 1973), were reported
present, respectively, by Schaefer (1998), on Aruba island very close to the Paraguaná Peninsula, which can be seen on
the horizon from Punta de Barco (actually 31 km off the peninsula coast; see Figure 2), and by the ARVAL Observatory
at this last observation site. According to the criterion given by Silverman and Mullen (1975) a dark eclipse can be
qualified as such if stars of third magnitude (mV = 3) can be observed. In comparing the above reported star sightings
with this criterion, it is certain that the eclipse here was not dark at all even in the centre line of the path where the
observation site was located. It is expected that this limit decreases due to a dependence of it on the distance to the nearest
edge of the shadow. The most probable cause explaining the results reported in this work resides in the influence of the
aerosol contained in the troposphere, on the scattering of light coming from the penumbra and in the umbra itself (see
Figure 3). It is well known that some of atmospheric aerosol species are hygroscopic, and their optical properties are a
strong function of relative humidity (Hegg et al., 1993; Tang, 1996). As this parameter increases during the total phase of
a solar eclipse leading to a decrease in water vapour content of the air (Bose et al., 1997), the wáter uptake by aerosols
also increases, and the scattering of light by them likewise. This can explain the fact that the extinction coefficient of
aerosols increases during the totality of an eclipse of the Sun, increasing the sky brightness at the same time. Moreover
the Paraguaná Peninsula (∼=2396 km2) is a semi-arid zone connected to mainland through a very narrow isthmus or strip
of land 30 km (18 miles) in length by 5 km (3 miles) in width, called the Isthmus of the Medanos (Figure 2). It is arid but
with some parts constituted by big and tall shifting sand-dunes called the Medanos of Coro (Coro city is the capital of
Falcón State) that have been formed by the gusting east winds. The tallest of these “Medanos” can reach heights over 25
m (81 ft), along the isthmus (as well as a small section of the continental coast nearby). Possibly the natural aerosol
background of the region
TABLE I
Global extinction coefficient values for different ambient conditions (Schaefer, 1986) kg (mag/air mass)
Description
0.10 Best night on dry mountain top
0.15 Average night on dry mountain top
0.20 Poor night on dry mountain top
0.20 Best night at dry sea level site
0.25 Average night at dry sea level site
0.25 Best night at humid sea level site
0.30 Average night at humid sea level site
0.40 Average night at poor site with much dust or humidity
0.50 Very poor night
These descriptions are provided so that estimates of the average can be deduced in the absence of better data.
Variations around the stated mean will occur at different sites, times of day, and times of year. A “dry sea level site”, for
example, may have quite clear skies or it may have morning hazes or it may have substantial amounts of windborn dust.
The user should guard against known climate change. is a mixture externally composed of marine hygroscopic aerosol
and dust particles from these sand-dunes aloft with a high scattering altogether. During the eclipse the effect referred to
above could have been enhanced by an additional increase of the normal aerosol background of the zone, due to the
presence of thousands of cars, coaches, and other motor vehicles which visited the Peninsula. It seems probable that it
could contribute to make the aerosol internal mixture more complex but not enough to increase appreciably the aerosol
concentration in the area as to be considered highly polluted.
It is interesting to note that a few previous works have been enough to demonstrate the influences of the
meteorological parameter changes upon atmospheric aerosol properties as a consequence of solar eclipses.
Perhaps Maske et al. (1982), Manohar et al. (1985), and Fernández et al. (1993) were the first authors in revealing direct
and indirectly these influences, in particular, from the solar eclipse of 16 February 1980 in India (Fiala and Lukac, 1978;
Bhattacharyya, 1978; Maske et al., 1982; Manohar et al., 1985) and from the solar eclipse of 11 July 1991 in Costa Rica
(Fernández et al., 1993).
In the report of Maske et al. (1982) observational results are presented indicating that an increases of the
concentration of suspended particulates was detected during this eclipse, being well above the usual range of suspended
matter in clean mountain air. In the same event, from the lowered atmospheric conductivity measurements made at
Raichur by Manohar et al. (1985), they suggested the formation of small particles due to high humidity conditions by the
eclipse forcing as the explanation for the atmospheric conductivity decreases and the subsequently increasing in the
atmospheric electric field: in the presence of such particles, small ions are lost through diffusion over the surfaces of these
particles leaving large ions that produce a shift in the size distribution from small ions to large ions.
Interestingly, from the measurements made by Fernández et al. (1993) of direct solar radiation during the 1991
solar eclipse in Central America (Fernández et al., 1992), they were able to deduce an increasing of aerosols in the
atmosphere through an analysis of the Ångstrom’s parameters (turbidity coefficient β and growth exponent α), thus
corroborating the finding of Maske et al. (1982). As a response to the totality these parameters acquired unusual values
varying in opposite directions, β rising and α diminishing in the indicated interval. According to their explanation this is
indicative of a presence of a high number of large particles in comparison with a low number of small particles. As
mentioned above, they agree that aerosols may have been salt particles from the sea and dust particles from the ground.
The efficiency of such particles as condensation nuclei depends on their properties.
Hygroscopic particles are of special interest: When RH is high, they absorb wáter and grow. Therefore, their size
augment during the eclipse as temperature falls sensibly; as a result, RH rises in a comparatively short time, effect this
that, in passing and historically speaking, was already noted as early as 1927 precisely in the solar eclipse of 29 June but
at Jokkmokk, northern Sweden, on the Arctic Polar Circle (Stenz, 1929).
Later reports on direct atmospheric aerosol measurements under solar eclipse situation correspond to Dani and
Devara (1996), Sapra et al. (1997a,b), Niranjan and Thulasiraman (1998), Bansal and Verma (1998) and Singh et al.
(1999) which dealt with the solar eclipse of 24 October 1995 also in India (Espenak and Anderson, 1994).
In the second and third of these works a 2–4 fold increases in the aerosol number and mass concentration,
occurred mainly in the sub-micron size and after a time lag of about 80 min from the beginning of the eclipse, were
reported at Bhabha Atomic Research Centre in Trombay where the phenomenon reached a partial maximum
of 72% obscurity.
In the fourth one, Niranjan and Thulasiraman (1998), working with a network of 5 multiwavelength
radiometers, detected an increases of the aerosol optical depth in a tropical site located on the east coast of India
(Visakhapatnam) as a result of a change in the local meteorological parameters, associated with the reduction in the solar
flux due to a total solar eclipse. Certainly this increases is related to a change in the optical properties of the coastal
aerosol due to a change in the ambient relative humidity. They also reported a change in the aerosol size distribution.
Similar results, found at Robertsgunj (Uttar Pradesh), were previously reported in the first of these works (Dani and
Devara, 1996).
Observations made at Roorkee (90–92% maximum obscurity), described in the last two of these reports, also
concluded that the aerosol concentration increased during the phenomenon.
Figure 14 depicts a general view of the variation of the extinction coefficient for the horizon direction, opposite
(anti-parallel) the shadow path, between 11:00 and 17:00 local time. It fluctuates in an irregular way between 0.99 and
0.09 mag/air mass, the average being equal to 0.57 (∼0.60) mag/air mass. In general irregular fluctuating behaviour is
typical for this coefficient in the troposphere, mainly in the boundary layer, on a daily basis. By applying Equation (13) a
gross mean value of 0.55 for the optical depth was found in that particular direction along that day. Note that during the
total phase, and after the third contact (14:13:02, local time) an increase of the extinction coefficient is detected as a
consequence of the atmospheric response to the eclipse; this result is consistent with that obtained for the global total
extinction coefficient at Punta de Barco (see Figure 15) and with that expected to happen during and just after this phase
(Maske et al., 1982; Fernández et al., 1993; Dani and Devara, 1996; Sapra et al., 1997a, b; Niranjan and Thulasiraman,
1998).
Figure 14. Variation of the extinction coefficient in the horizon direction, opposite (anti-parallel)
the shadow path, between 11:00 and 17:00 local time, the day of the eclipse. The values are gross
estimates. However this profile can portray or represent the variation of this parameter at that day,
and in that direction. Note that during the total phase, and after the third contact (14:13:02, local
time) an increase of the extinction coefficient was detected.
Figure 15. The shadow path of the total solar eclipse of 3 February 1916 through Venezuela. Tucacas
town is located on the coast, and Barquisimeto city is about the centre of the map. Both are indicated
as a black dot (map reproduced from Ugueto’s report).
7. Comparison with the Total Solar Eclipse of 3 February 1916 As mentioned earlier, the total eclipse of 3
February 1916 was the first total solar eclipse observed from Venezuela in the last century. The shadow path can be seen
in Figure 15. Coincidentally it also passed over Falcón State and occurred on a Thursday in a similar month as it was for
1998. A special expedition from the Cagigal Observatory of Caracas went to a small coastal town called Tucacas
(68◦18_13.5__ W, 10◦47_37.9__ N, 0 m above sea level) to make astronomical, atmospheric and meteorological
observations a few days previous to the eclipse and during that day (Ugueto, 1916). The local circumstances for this
location as deduced observationally by the expedition were: first contact at 9:55:28.6, second contact at 11:26:48.6, third
contact at 11:29:19.8, and fourth contact at 13:00:51.2, all these times being given in local time (UT-4.30 at that time).
The totality lasted ∼2 min 24 s. The atmospheric conditions for the eclipse day were described as very good although
some clouds were present momentarily at 11:15. A variation in temperature of −9.2 ◦C was noted between 10:05 and
11:25 (local time). For Tucacas town Equation (6) and Equation (9) remain the same and Equations (7)–(8)
are reduced to,
koz = (0.031/3.0){3.0 + 0.4[0.19 cos(αs) − 0.84]}, (14)
ka = 0.12[1 − (0.32/ ln S)]4/3[1 + 0.33 sin(αs)], (15)
to find, according to Equation (1), the total extinction coefficient in the visual for that particular location during that
eclipse. The data for S and t were taken from Ugueto (1916), and the data for αs was calculated using the software by
Duffet- Smith (1997). Figure 16 presents the temperature measurements made the day of this eclipse by the Cagigal
Observatory team.
Figure 16. Variation of temperature during the eclipse of 3 February 1916 between 09:55 and 12:55
(local time), measured by the Cagigal Observatory team at Tucacas (Falc´on, Venezuela).
Figure 17 shows the extinction profile for each of the different components contributing to the total extinction as
well as the total extinction and relative humidity profiles. It can be seen that, again, the total extinction in the visual is
strongly dependent on aerosol extinction (ka _ kwv > kR > koz). During the totality a value of 0.78 mag/air mass for the
total global extinction coefficient in the visual was obtained at 11:25, indicating also a poor “night” (k > 0.5). In fact,
only Venus, Jupiter and Vega (α Lyr), with mV = 0.04 (Allen, 1973), were reported (Ugueto, 1916). In comparing this
result with that obtained for the total solar eclipse of 1998 at 14:12 (kg ∼= 1.11 mag/air mass), it can be inferred that the
eclipse of 1916 was darker than 1998’s by a factor of ∼0.70; in other words, 30% less bright. This outcome can be
appreciated better in terms of visual observations. During the totality of the 1916 eclipse the Cagigal Observatory team
could see just one star (Vega) which is less bright than those (Deneb and Fomalhaut) seen by the ARVAL
Figure 17. Profile of the global total extinction coefficient in the visual and those for each component contributing to it, during the
solar eclipse of 3 February 1916, at Tucacas town (Falc´on State, Venezuela) between the first and fourth contacts, calculated from
meteorological data provided by Ugueto (1916) and using the same model as in Figure 13. Note again that the total extinction profile is
controlled by the aerosol extinction profile. The water vapour profile is also included for comparison purposes.
Observatory team, and Schaefer (1998), respectively, during the totality of the 1998 eclipse. It is surprising, then,
that despite its closeness to Vega in the sky, Deneb, being brighter than Vega, was not reported as sighted by the Cagigal
team.
Because Tucacas town and Punta de Barco are hot places during the day and throughout the year, the change in
temperature during the central phase of the respective eclipses had to be appreciably noted even more for the times when
it occurred: the first one at the end of the morning, and the second one near the middle of the afternoon. The first one was
“fresher” than the other. In the first one the temperature descended from about 34.2 ◦C to 25 ◦C; in the second one
from about 30.9 ◦C to 25.2 ◦C. Consequently between both eclipses a significant difference of 4.2 ◦C in the reduction of
temperature was found.
It is fair to mention that the Cagigal group also made photometric measurements of the sky during the first part
of the eclipse. They used a Heyde aktino photometer which was calibrated with a lamp with only three readings.
Subsequently six measurements were made before the second contact, and just one during the totality.
The first one, at 09:20 (local time), gave 16.5 instrumental units, and at totality 1.5 instrumental units. Because the units
were not specified nor the sky area covered or direction to which their instrument was pointed, a photometric comparison
with the 1998 eclipse could not be made. Figure 18 gives a plot of their measurements from which can be seen the
reduction of the sky brightness.
Figure 18. Plot of the photometric measurements made by the Cagigal Observatory group of Caracas,
using a Heyde aktino photometer, of the sky brightness during the total solar eclipse of 3 February
1916 at Tucacas town (Falc´on State), Venezuela. Because the units were not specified, no comparison
could be made.
8. Overview and Conclusions
This paper presents the results of photometric measurements of the intensity of the sky brightness obtained
before, during, and after the total solar eclipse of 26 February 1998 at the Caribbean Peninsula of Paraguaná (Falcón
State) in Venezuela, in three particular directions: Zenith, horizon anti-parallel or opposite to the Umbra path, and horizon
perpendicular to this path. These measurements during the totality showed that there was a decrease of three orders of
magnitude in the zenith sky brightness as compared to that for noneclipse conditions on that day. Also it was observed
that there was a decrease in the horizon sky brightness, perpendicular to the shadow path, by the same order of magnitude
as compared with that for the normal day sky in this event. The directions considered on the horizon, and the period of
time covered, account for the asymmetry observed in the curves obtained before and after the totality. As a result,
consistent with those general obtained for total solar eclipses, the zenith brightness turned out to be less intense tan the
horizon. In particular, using the sky brightness at full Moon as a reference, the minimum value corresponding to the
horizon perpendicular to the shadow path was 36 times, and that to the zenith was ∼14 times brighter, respectively. The
zenith brightness during the totality turned out to be 4 times brighter than that measured OPTICAL RESPONSE OF THE
ATMOSPHERE DURING SOLAR ECLIPSES by James (1998) for the same location. As in previous eclipses, the
change in this brightness began to be appreciable when the solar disc was obscured 98.81%. This paper also presents, in
global terms, an estimate of the total extinction coefficient in the visual and their components, produced by Rayleigh
scattering, ozone, water vapour and atmospheric aerosol extinction. The results show that atmospheric aerosol is the
major component contributing to the total extinction coefficient in the visual, and ozone is a minor one. During the
totality this coefficient
attained a value of 1.11 mag/air mass which indicates that the darkness produced was indeed very poor. Besides three
very bright planets which were clearly seen close to the Sun, only two bright stars were reported to have been sighted at
the same time. Therefore, as a first conclusion, the most probable cause explaining this result is the influence of the
atmospheric aerosol scattering on the sky brightness during the total phase of the eclipse.
This conclusion is supported by comparisons made with the total solar eclipse of 3 February 1916. The results
obtained show that the total global extinction coefficient in the visual is strongly dependent on atmospheric aerosol
extinction and less on ozone. During the totality a value of 0.78 mag/air mass was estimated for this coefficient indicating
that the darkness produced in that eclipse was also poor. Only one bright star was reported along with three bright planets
in the sky of the observation site. Even so, and as a second conclusion, this eclipse was 30% darker than 1998’s. Also the
temperature variation was greater in the first one than in the second one.
In addition to the above estimates, photometric measurements were used to make estimations of the extinction
coefficient (within at least 20% accuracy) before, during, and after the phenomenon for the horizon direction, opposite the
shadow path, in the visual. From these estimations a calculation of the mean optical depth in that particular direction was
made. The results indicate that the extinction coefficient fluctuated in an irregular manner (between ∼0.1–∼1.0 mag/air
mass) for the horizon direction. On average a value of ∼0.60 mag/air mass was found. The corresponding value for the
optical depth was 0.55. An increase of the extinction coefficient during and after the total phase was detected.
It has been photometrically demonstrated that the sky during the totality of the 1998 eclipse was very bright on
the horizon as well as at the zenith. This is corroborated by direct visual observations made by this author and by others in
the same area which point out that only three planets and only two bright stars could be seen. This general result has in
turn been corroborated by applying an empirical model in which astronomical and meteorological data was used. By
taking into account the two eclipses considered here, it seems in general terms that, observing phenomena of this type just
near the sea, brighter skies are produced during the totality. This conclusion is supported by the results reported by
Niranjan and Thulasiraman (1998) of the tropical total solar eclipse of 24 October 1995 for a seaside location on the east
coast of India, along with the results reported by Fernández et al. (1983) of the tropical total solar eclipse of 11 July 1991
for some towns along the west coast of Costa Rica on the Pacific Ocean.
It is highly recommended, using future total solar eclipses, to make spectral measurements of the radiance of the
eclipsed sky, towards the zenith, in order to attempt additional tests such as those made by Shaw (1978, 1979) of his
model (Shaw, 1978). Near the horizon a model explaining the sky colour during a total solar eclipse has been proposed by
Gedzelman (1975), which evidently depends on wavelength. In future eclipses of this type an experimental verification of
this model is also suggested and expected because so far none has been done.
The central focus of this paper has been first to put emphasis in the influence exerted by atmospheric aerosol on
the sky brightness during a tropical total solar eclipse, by using astronomical and meteorological data in an empirical
model, and second, along with direct visual reports of stars and planets, to present consistent photometric measurements
of this brightness. Nonetheless, based on the work of Darula and Kittler (2000), and Shiozaki et al. (1999), an alternative
and interesting approach to study daylight levels at the crucial stages of a solar eclipse has recently been published by
Darula et al. (2001) which has been applied by them to the partial solar eclipse of 11 August 1999 over Athens and
Bratislava. In the special and extreme case of an eclipsed rising sun, Liu and Zhou (1999) have developed an empirical
model to estimate the sky brightness for analysing the curious optical effect known as “double dawn” (Stephenson, 1992;
Liu et al., 1999).
Possibly past total solar eclipses were darker (Schove and Fletcher, 1987) than the present ones in populated
areas given the anthropogenic alteration of the particle composition of the air today. People at the beginning of the last
century, and earlier, could enjoy more this kind of phenomenon from cities and towns. Quoting Ugueto’s historical report
of 1916 (in translation from the Spanish): “Through the different phases of the eclipse the book known as “Connaissance
des Temps” was set to a distance so that the title on a blue background could be read easily by an observer with normal
sight and in broad daylight; the following observations were obtained: At 10h 31m one could read it from 4 metres, at 11h
5m from 3 metres, and during the totality from 0.80 to 1 metre”. From another report (del Castillo et al., 1916)
of the observation of the same eclipse in Venezuela, but for a different location (Barquisimeto city; see Figure
15), the following statement was written (in translation from the Spanish): “At the moment of the totality one
could read, even though with some little effort. On the Imitation of Christ, trans. by Fray Luis de Granada, B.
Herder Ed., Friburgh, 1905 [8 point types] one could not read it; and on the History of the Earth by L. de
Launay, José Ruiz Ed. Madrid, 1907, [12 point types] it could”. Following the division proposed by Silverman
and Mullen (1975) it seems that the 1916 eclipse, at Tucacas, can be classified as a light eclipse. A dark
eclipse, on the contrary, is that in which print, dials, objects, etc., cannot be distinguished according to this
division.
For the 1998 eclipse at Punta de Barco James (1998) reported that small numbers and markings on cameras and
lenses, which had been completely invisible during totality from Chile in 1994 (the specific location was not specified),
were easily seen at that location; this, in turn, classifies the 1998 eclipse at Punta de Barco as a light eclipse too.
As expected (Meeus, 1982), it will take a long time before another total solar eclipse takes place in Venezuela. Although
this will not occur for another 72 years, on 28th September 2071, it is to be hoped that the results presented in this work
will contribute to the series of solar eclipse studies in this country started with the pioneering reports on the eclipse of 3
February 1916 and that will keep their continuity in time.
Acknowledgements
First I wish to acknowledge in Venezuela the indispensable financial support provided by the Fundación Polar
(Caracas) to cover international and national travel expenses; their co-operation is highly appreciated. Also this
acknowledge is extended to Prof. C. Noguera, Faculty of Engineering, Universidad Central (Caracas), and his eclipse
team, who provided transport and logistic assistance. Particular thanks are given to Ing◦. V. Castro and relatives, wardens
of the “Radio Nacional de Venezuela” booster station at Punta de Barco (Paraguaná, Falcón), for his hospitality,
friendship, and logistic support. Thanks are also due to Lic. F. Galea of the Biblioteca Central, Universidad Central
(Caracas), who kindly provided a copy of the Ugueto’s report of 1916 eclipse, and a copy of del Castillo’s 1916 eclipse
report.
I am also indebted to A. Valencia, A. Arnal, and A. Laya of ARVAL Observatory team (Caracas) for providing
the meteorological data from their web site, the map of Paraguaná Peninsula presented in this work, and bibliographical
assistance. In England, at the University of Essex, I am grateful to Dr. S. Nogues, and Mr. P. Beckwith for their
assistance in calibrating the equipment. Mr. T. Trill also gave additional technical support. Mr. T. Vigors and Mr. S.
Doubtfire gave very useful computing assistance. Dr. I. Colbeck provided valuable additional financial and administrative
support and supplied the equipment used in this work. Also I wish to thank him, along with Mr.M. O’Really, for their
collaboration in the revision and correction of the typescript. Dr. D. H. Fremlin and Dr. E. Izquierdo made fruitful
mathematical comments. In the United States special thanks are given to Dr. S. Silverman and Dr. J. M. Pasachoff for
providing important bibliographical material and scientific information, to Dr. B. Schaefer for his valuable discussion and
comments which contributed to improve this paper, and to Dr. F. Espenak for his kindly help in providing eclipse
obscuration and other 1998 eclipse calculations.
Mr. P. Poitevin helpfully provided a copy of the Sifontes’ report from Belgium. Dr. E. Hanna, Dr. B. K. Sapra
and Mr. G. Comello supplied relevant references from England, India and The Netherlands, respectively. The University
of Los Andes (Mérida-Venezuela), through CELCIEC (Fac. Ciencias), helped to post-edit the figures.
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Kepler 62e y 62f Planetas Acuosos
"Estos planetas no se parecen a nada en nuestro sistema solar. Están cubiertos con océanos infinitos", dijo Lisa
Kaltenegger, del Instituto de Astronomía Max Planck, que estudió los planetas.
Se trata de los dos planetas de la estrella Kepler-62, que se encuentra a 1200 años luz de la Tierra, en la
constelación de Lira. Dos de sus cinco planetas, llamados Kepler-62e y Kepler-62f, están en la zona habitable de la
estrella, es decir, están a una distancia de su
sol que les permite mantener la temperatura
necesaria para que exista el agua en estado
Líquido lo que es imprescindible para la
aparición de la vida.
En estos planetas hay agua y mucha.
La vida podría existir, por tanto, pero no se
sabe si podría existir alguna civilización.
"La vida en estos planetas debería
sobrevivir debajo del agua, lo que hace difícil
conseguir los metales, desarrollar la
metalurgia y crear la electricidad requeridos
para la existencia de una civilización", señala
Kaltnegger.
"Sin embargo, los mundos podrían
tener una gran belleza, con un océano azul
bajo un sol de color naranja. Y quién sabe,
quizá podría existir vida lo suficientemente
inteligente para desarrollar tecnología hasta
un nivel que nos sorprendería", añade
Kaltnegger.
Búsqueda de Agua en otros Planetas
Jesús H. Otero A.
La búsqueda de agua en los planetas extrasolares será más precisa y menos cara gracias a un nuevo método
creado por astrónomos europeos.
Lo que hicieron Jayne Birkby de la Universidad de Leiden y sus colegas fue poner al revés el método actual para
buscar agua en los exoplanetas. Ahora los astrónomos estudian las fluctuaciones de la radiación de la estrella causada por
la gravitación del planeta, pero Birkby estudió los cambios del espectro del planeta provocados por la estrella.
Los astrónomos comprobaron con éxito su técnica estudiando el planeta gigante HD 189733b en la constelación
de la Zorra (Vulpecula). Este gigante gaseoso, localizado a 63 años luz de la Tierra, tiene una temperatura que alcanza
unos 1500 grados, y está muy cerca de su estrella, a la que orbita en dos días. Anteriormente se encontraron agua y
monóxido de carbono en su atmósfera, así que era un buen candidato para comprobar el método.
La nueva técnica hará una búsqueda de agua y de otros elementos cruciales para la existencia de vida más
precisa y 'barata', ya que se podrán usar los telescopios en la Tierra en vez de los telescopios espaciales. Los científicos
esperan que el telescopio E-ELT, cuyo lanzamiento está previsto en 2020, tenga la resolución requerida para buscar agua
en los planetas más pequeños, parecidos a la Tierra.
Punto de Inflexión
Avaaz
La última era de hielo ocurrió en seis meses. En solo seis meses, el planeta desató un ejército de bloques de
hielo tan grandes como edificios por toda Europa y Estados Unidos. Fue un punto de inflexión climático que rompió el
equilibrio del planeta por completo y puso en riesgo la supervivencia de todo y de todos. Ahora estamos al borde de vivir
Tres puntos de inflexión iguales a este.
En palabras de un destacado científico de la NASA, estamos ante un momento en el que podemos irnos al
carajo. Ante este horrendo panorama, solo nos queda reaccionar ahora mismo de forma masiva y coordinada para
cambiar el futuro que nos espera.
Un acuerdo global con pasos básicos para acabar con las energías contaminantes puede salvarnos. Es por ello
que la ONU ha convocado una reunión urgente sobre el cambio climático con los principales líderes del mundo en poco
más de 100 días. Si les recibimos el 21 de septiembre con la movilización global por el medio ambiente más grande de
la historia, podremos romper el poder de las megas mineras, y petroleras que están impidiendo que incluso los mejores
políticos hagan lo correcto.
Es imposible ignorar el peso de esta tarea. Pero cada pequeña acción unida a la siguiente se traducirá en la fuerza
de millones de personas, ahogando las voces de los opositores y dando a nuestros jefes de gobierno la razón más
poderosa para reaccionar ya y construir juntos un futuro limpio, verde y lleno de esperanza. Haz clic abajo para unirte:
Los "puntos de inflexión" son espirales que se retroalimentan, donde el cambio climático revierte sobre sí
mismo, provocando consecuencias catastróficas
aceleradas. Ahora mismo, el gas metano, que es 25
veces peor que el CO2 para el cambio climático,
está congelado debajo del hielo. Pero, a medida que
el hielo se derrita, el gas se filtrará, causando un
deshielo aún mayor. Cada deshielo nos hace perder
otro de los escudos reflectantes que utilizamos para
mantener el planeta fresco. En otras palabras, más
metano y menos hielo aumentarán el cambio
climático y todo empezaría a salirse fuera de
control. Y éste es solo un ejemplo. Por eso los
científicos han subido el tono y están pidiendo a
gritos que actuemos ya.
Aunque parezca desolador, tenemos las
herramientas y sabemos cuál es el plan necesario para asegurarnos de que no caigamos en un punto de no retorno que
acabe con nosotros del todo. Y, aunque requerirá una cooperación global de una envergadura mayor que nunca, nuestro
movimiento de 36 millones de miembros tiene el poder ciudadano necesario como para motivar a los líderes de
cada país a que den los primeros pasos.
Está creciendo la expectativa sobre la cumbre climática de Paris 2015, donde se podría sellar un acuerdo global.
Justamente hace unos días, Estados
Unidos y China anunciaron nuevos planes
para frenar la contaminación en sus
países. En solo 100 días nosotros
podemos dar un paso a otro nivel.
Ocupar las calles es una de las
herramientas más efectivas para crear
cambio social porque demuestra poder,
unión y coordinación en tiempo récord. A
veces es la única vía: hay ejemplos
clásicos como el movimiento antiApartheid de Sudáfrica hasta la lucha por
los derechos civiles en los EE UU. Es el
momento de aplicar ese poder al asunto
más importante de nuestro tiempo: la
supervivencia y un futuro próspero para
nuestras familias, sus familias y las
generaciones venideras.
Evidence for solar wind modulation of lightning
C J Scott, R G Harrison, M J Owens, M Lockwood and L Barnard
CJ Scott et al 2014 Environ Res. Lett.9 055004 C J Scott IOP Publishing Ltd
Abstract
The response of lightning rates over Europe to arrival of high speed solar wind streams at Earth is investigated
using a superposed epoch analysis. Fast solar wind stream arrival is determined from modulation of the solar wind V y
component, measured by the Advanced Composition Explorer spacecraft. Lightning rate changes around these event
times are determined from the very low frequency arrival time difference (ATD) system of the UK Met Office. Arrival of
high speed streams at Earth is found to be preceded by a decrease in total solar irradiance and an increase in sunspot
number and Mg II emissions. These are consistent with the high speed stream's source being co-located with an active
region appearing on the Eastern solar limb and rotating at the 27 d period of the Sun. Arrival of the high speed stream at
Earth also coincides with a small (~1%) but rapid decrease in galactic cosmic ray flux, a moderate (~6%) increase in
lower energy solar energetic protons (SEPs), and a substantial, statistically significant increase in lightning rates. These
changes persist for around 40 d in all three quantities. The lightning rate increase is corroborated by an increase in the
total number of thunder days observed by UK Met stations, again persisting for around 40 d after the arrival of a high
speed solar wind stream. This result appears to contradict earlier studies that found an anti-correlation between sunspot
number and thunder days over solar cycle timescales. The increase in lightning rates and thunder days that we observe
coincides with an increased flux of SEPs which, while not being detected at ground level, nevertheless penetrate the
atmosphere to tropospheric altitudes. This effect could be further amplified by an increase in mean lightning stroke
intensity that brings more strokes above the detection threshold of the ATD system. In order to remove any potential
seasonal bias the analysis was repeated for daily solar wind triggers occurring during the summer months (June to
August). Though this reduced the number of solar wind triggers to 32, the response in both lightning and thunder day data
remained statistically significant. This modulation of lightning by regular and predictable solar wind events may be
beneficial to medium range forecasting of hazardous weather.
Content from this work may be used under the terms of the Creative Commons Attribution 3.0 licence. Any
further distribution of this work must maintain attribution to the author(s) and the title of the work, journal citation and
DOI.
1. Introduction
The Sun undergoes an approximately 11 year activity cycle driven by the differential rotation rate of the solar
convection zone. This differential rotation of the solar plasma distorts the solar magnetic field, gradually converting a
polar field into a toroidal one throughout the solar cycle (Babcock 1961). As the magnetic field becomes more distorted,
complex regions of intense magnetic field emerge through the photosphere. Observed in visible light, the emerged
magnetic flux tubes with larger diameters appear darker than the surrounding photosphere and are known as sunspots.
Solar influences on the terrestrial atmosphere, and, in particular, effects on electrified storms have been studied for many
years, as summarized by Schlegel et al (2001). Stringfellow (1974), found a correlation between sunspot number and day
on which thunder was heard ('thunder days') in the UK while other studies (Pinto et al 2013) have found an anticorrelation between solar cycle variations and thunder days. Brooks (1934) analysed data from a variety of locations and
found a large variation in the relationship between sunspots and thunderstorm activity. Markson (1981) demonstrated a
positive correlation between galactic cosmic ray (GCR) flux and ionospheric potential which, it has been argued,
indicates a sensitivity of thundercloud electrification to ambient electrical conditions. Mechanisms have subsequently
been postulated by which solar activity could influence the frequency of terrestrial lightning through modulation of the
solar irradiance, the GCR flux or some combination of these two. These are discussed below.
Increase in GCR flux may directly trigger lightning through 'runaway breakdown' of electrons, leading to
breakdown (Roussel-Dupré et al 2008). This is supported by recent observations of energetic photons from
thunderstorms, as predicted by runaway breakdown theory (e.g. Gurevich and Zybin 2005). In a study using 16 years of
lightning data over the USA, Chronis (2009) found lightning activity dropped 4–5 d after a transient reduction in GCRs (a
Forbush decrease), with a positive correlation between lightning and GCRs during the winter. Before the final triggering
of lightning however, an increase in atmospheric ionization may also reduce the effectiveness of thunderstorm charging
processes. In the extreme case of a simulated nuclear winter, in which atmospheric ionization was assumed to be vastly
increased, Spangler and Rosenkilde (1979) estimated that charging of thunderstorms would be inhibited. However,
following the Chernobyl reactor accident, in which lower troposphere ionization increases occurred, an increase in
lightning was observed as radioactivity passed over Sweden, so the response may be complex (Israelsson et al 1987). For
example, changes in atmospheric conductivity also occur with natural variation in cosmic ray ionization (Harrison and
Usoskin 2010). Hence establishing the sign of the response in lightning to GCRs may therefore be complicated by
competing processes, in which different regional meteorological characteristics also play a role. The analysis here uses
well-defined marker events in the solar wind to investigate the response in lighting over the UK, as detected by a very
low frequency lightning detection system.
2. Solar modulation of GCRs
While most of the solar atmosphere is retained by gravity, energetic particles can still escape and form a
continuous stream of plasma into interplanetary space known as the solar wind. There is also an extremely energetic, but
intermittent, population of particles known as solar energetic protons (SEPs). The solar wind speed varies between 400
and 2000 km s−1 and is modulated by the local solar magnetic field at its point of emergence. Source regions connected to
the heliospheric magnetic field (HMF) through 'open' field lines are associated with high speed solar wind streams while
source regions with 'closed' magnetic topology are associated with slow solar wind streams. Despite differential rotation
of the solar convection zone and surface, the magnetic field in the solar atmosphere means it rotates as if it were a solid
body, resulting in a modulation of the solar wind at Earth of a period close to 27 d as fast and slow solar wind streams
sweep past our planet. The passage of a fast solar wind stream also generates a temporary enhancement in plasma density
and magnetic field strength of the solar wind at Earth called a 'co-rotating interaction region' (CIR) which further
modulates the GCR flux (Rouillard and Lockwood 2007). Because CIRs persist for several solar rotations the decreases
in GCR flux they cause tend to recur at Earth every 27 d, whereas the transient Forbush decreases do not.
Transient Forbush decreases at Earth are caused by the passage of coronal mass ejections (CMEs). A CME is
generated after a reconfiguration of complex regions of magnetic field in the solar atmosphere which result in vast
magnetic 'clouds' of solar plasma erupting into interplanetary space. A typical CME contains around one billion tonnes of
material travelling at up to 2500 km s −1. The CMEs add to the quiet solar wind outflow driven by the high temperatures of
the solar atmosphere and as CMEs and the solar wind propagate away from the Sun, they extend the solar magnetic field
into interplanetary space where it becomes known as the HMF. The occurrence rate of CMEs is modulated by the solar
activity cycle, with more occurring at solar maximum. The relative strength of the HMF is therefore greater at the peak of
the cycle (Owens and Lockwood 2012). The HMF modulates the flux of highly energetic particles, GCRs, which are
pervasive throughout the solar system. These particles have been accelerated to such high energies (typically 0.5 GeV–
100 GeV) by extreme events in the Universe such as supernovae. On entering the Earth's atmosphere, these particles
collide with gas particles, generating neutrons that can be detected by monitoring stations on the ground (e.g. Usoskin et
al 2009). The GCR flux measured in this way is inversely proportional to the strength of the HMF, which in turn
approximately follows solar activity and sunspot number (e.g. Rouillard and Lockwood 2004). The passage of a CME
past Earth is known to further modulate the GCR flux as it brings with it a localized cloud of magnetized plasma. This
enhanced field results in a temporary reduction in the GCR flux, (a Forbush decrease) used as marker events for
comparison with lightning in the study of Chronis (2009).
While Earth-directed CMEs generate the largest Forbush decreases in cosmic ray flux, there are relatively few of
these events in any given solar cycle. In their analysis, for example, Usoskin et al (2008) identified 39 strong Forbush
decreases in data from the World Neutron Monitor Network since 1964. Instead, in this paper, we consider the arrival of
high-speed solar wind streams at Earth from 2000 to 2005 and combine these in a superposed epoch analysis to look for a
modulation in lightning rates in data from the arrival time difference (ATD) lightning detection network of the UK Met
Office (Lee 1989). While these solar wind streams cause smaller decreases in GCR flux than CMEs, they are sufficiently
numerous to allow a meaningful statistical analysis (for comparison, Usoskin et al (2008) identified 14 Forbush events
between 2000 and 2005).
3. Method
3.1. Identifying trigger events
The arrival of high speed solar wind streams at Earth can be inferred from sudden changes in the V y component
of the solar wind in the Geocentic-Solar-Ecliptic (GSE) frame of reference i.e., anti-parallel with the Earth's orbital
direction (e.g. McPherron et al 2004; Denton et al 2009; Davis et al 2012). Here we used solar wind data from the
Advanced Composition Explorer (ACE) spacecraft (Stone 1998), orbiting the L1 Lagrangian point 0.01 au upstream from
the Earth in the solar wind, along the Sun–Earth line (the X direction of the GSE frame). Arrival of a high-speed stream at
Earth was identified if the solar wind V y component increased by more than 75 km s−1 over 5 h. While the exact V y
threshold used is arbitrary, our results are robust to different choices; the threshold described presents a good
compromise, generating 532 pronounced events.
These event times were used as markers around which responses in other solar wind and geophysical parameters
were averaged, which is essentially the super-posed epoch or compositing technique originally described by Chree
(1908). Compositing provides a useful way of investigating weak yet repeated signals that may otherwise be swamped by
larger random variations. By aligning the secondary data according to the times identified in the primary data (the 'trigger'
times) and calculating the median response, random responses will average out to zero while any (even small but)
consistent signal will remain. Medians rather than means are calculated to ensure that the combined result is not
dominated by one or more large outliers in the data. In our study, 'trigger' times were the times at which enhancements
were observed in the solar wind V y component. Repeating the analysis many times using random trigger times, the
probability of whether a given response exceeds that expected by chance can be found by calculating the 95 and 99
percentiles of these random responses. The significance of any response can be further investigated by comparing the data
used to calculate median values at a range of times before and after the 'trigger' time using a two-sided
Kolmogorov−Smirnov test.
3.2. Geophysical parameters considered
In our study we first ensured that we were correctly identifying the arrival of solar wind streams by calculating
the median solar-wind velocity, V y, and magnetic field strength, B t from periods of data corresponding to an interval of
60 d around the trigger times identified. These times were then used to calculate the associated median variability in solar
parameters (total solar irradiance (TSI), sunspot number, Mg II emission, SEP flux and GCR flux), terrestrial lightning
rates and thunderstorm activity.
The speed and density of the solar wind were calculated using data from the NASA ACE Spacecraft (Stone et al
1998). The associated variations in TSI, sunspot number and Mg II emissions were used to investigate whether there was
any solar variation associated with the generation of high-speed streams. The TSI data used is the PMOD composite of
observations (Fröhlich 2006) which is consistent with other solar indicators and with irradiance modelling in its long-term
behaviour (Lockwood and Fröhlich 2008). The Mg II emission index (Heath and Schlesinger 1986) was included in this
analysis as this is often used as a proxy for many UV emissions (Viereck et al 2001).
Information about the solar wind energetic particles or SEPs was obtained from the GOES dataset (GOES N
Databook 2006), which combines data from several spacecraft. Proton energies are recorded in seven channels, each
identified by its low energy detection threshold. They are; > 1 Mev, >5 Mev, >10 Mev, >30 Mev, >50 Mev, >60 Mev and
>100 Mev.
The GCR flux incident at Earth was determined using data from the neutron monitoring station at Oulu
(Kananen et al 1991). This flagship dataset is a widely-used standard within the solar-terrestrial physics community. It is
a continuous, well-calibrated dataset, which, because of the station's high latitude location, records cosmic rays of
energies down to the atmospheric cut-off of about 1 GeV (at lower latitudes, the geomagnetic field shielding gives higher
cut-off energies).
Lightning rates were obtained from the ATD system of the UK Met Office (Lee 1989). This system uses a series
of radio receivers located around Western Europe to detect the broad-band radio emission emitted by lightning. Accurate
timing of the arrival of such 'sferics' at a range of stations allows the location of lightning to be determined with an
accuracy of 5 km over the UK. The ATD system has been designed to have greatest efficiency in detecting cloud-toground (CG) lightning over Europe. The current study uses ATD data between September 2000 and June 2005, as this
represents a period when the detection sensitivity of the system was not subject to modifications influencing its
sensitivity. After this period the system was expanded and increased in sensitivity to form ATDnet, which detects a much
larger number of smaller sferics. While the ATD system from 2000–2005 was capable of detecting lightning worldwide,
the sensitivity of the network was reduced for large distances. In order to ensure some uniformity of the lightning
measurements within our analysis we therefore restricted our data to any event that occurred within a radius of 500 km
from central England. The time range of the ATD data used in this study encompasses 405 of the 532 trigger events
identified in the ACE spacecraft data.
The presence of thunderstorm activity is also recorded at manned UK Met Office observing sites.
Conventionally, a 'thunder day' is considered as any day on which thunder was heard at an observing site. While this
observation is subject to false positives (such as vehicle noise or explosions being misidentified as thunder) and is of a
lower time resolution compared with the lightning data, it provides an independent measure of the presence of
thunderstorm activity on a given day.
4. Results
After identifying when high-speed solar wind streams arrived at Earth (as described in section 3.1), these times
were used to define t = 0 in all the geophysical datasets and the median response was calculated for each parameter as a
function of event time t for ±60 d around this time.
4.1. Solar wind
Figure 1 presents the median change in solar wind parameters measured by the ACE spacecraft. The top panel
shows the distribution of 'trigger' events within the epoch under consideration. As expected, the maximum number of
triggers (532) is seen at event time t = 0. Plotting the distribution of triggers used in this study demonstrates that there are
no other times within 60 d of the trigger time at which there is such a large number of high-speed streams arriving at
Earth. This is demonstrated by the middle panel of figure 1 in which the median response in the solar wind V y component
is presented. Around event time t = 0, the tangential solar wind decreases from a background level just below 0−35 km s −1
and then increases to over 60 km s−1, all within a period of around 2 d, with the greatest change at time zero. The grey
band, in this and subsequent plots, represents the standard error in the median for all the data points within each time bin
of the composite analysis. Outside this time window there are no other changes in V y that greatly exceed the 95 and 99
percentiles of the data (represented by the dot-dashed and dashed lines respectively) though there is a hint of the solar
rotation rate with slight enhancements in V y at ± 27 d and ± 54 d. These percentiles were estimated by repeating the
composite analysis one hundred times using the same number of trigger times drawn at random from within the scope of
the study. The percentiles were then estimated by sorting the distributions in each time bin and ascertaining the 95 and 99
percentiles. The bottom panel of figure 1 shows the associated median change in magnetic field strength associated with
high-speed solar wind streams. At t = 0, the total magnetic field strength, B t, peaks at about 13 nT compared with the
background of around 6 nT. The field rapidly increases and decays over 2 d around the peak. Other than this peak around
t = 0, there are no significant enhancements in the median solar wind magnetic field magnitude though again there are
hints of the solar rotation rate in enhancements at ±27 d and ±54 d.
Figure 1. The response of solar wind parameters in a superposed epoch analysis using enhancements in ACE V y
data as the trigger times, during 2000 to 2005. The top panel presents the number of triggers within each hourly time bin
of the superposed epoch analysis. 532 events were identified in the ACE solar wind data corresponding to times at which
the V y component of the solar wind increased by more than 75 km s−1 in 5 h. Such an enhancement is indicative of the
arrival of a high-speed solar wind stream at Earth. The middle panel contains the median response of the V y component
of the solar wind as measured by the ACE spacecraft. In this, and subsequent plots, the median response is represented by
a solid line, the standard error in this median as a grey area around the line while the dashed lines and the dotted lines
correspond to the 95% and 99% levels of the dataset respectively. These percentile levels were calculated by repeating the
analysis many times using random trigger times and determining the levels in each time bin that contained 95 and 99% of
the data points. The lower panel contains the median response in the magnitude of the interplanetary magnetic field, B t.
4.2. Solar irradiance
Three associated measures of solar activity are compared in figure 2. The median TSI (figure 2, top panel) shows
a small (0.01%) but significant decrease some 7 d ahead of the arrival of fast solar wind streams at Earth. This decrease is
associated with a rise in the median sunspot number, which lasts for around 12 d. This is the time taken for half a solar
rotation (13.5 d) with respect to the Earth and is likely to be caused by the appearance and rotation of active regions on
the solar surface. In the photosphere, active magnetic regions manifest themselves as sunspots—darker cooler regions
where the convection of the plasma has been suppressed by the strength of the local magnetic fields. Sunspots have been
used as a proxy of solar activity for many hundreds of years. The peak sunspot number and minimum TSI will, on
average, be when the sunspots are close to the centre of the solar disk and this occurs between t = −6 d and t = −4 d which
is close to the delay expected for the (radial) solar wind from such a region to reach Earth. The complex magnetic field
topology around such regions is likely to lead to areas of open solar flux along which fast solar wind streams can emerge
and so it is not unexpected that the two phenomena should be linked. The bottom panel of figure 2 presents the median
Mg II index of solar emission. This broad emission, centred on a wavelength on 279.9 nm, has been found to be a
convenient proxy for UV emissions at other wavelengths. It presents similar behaviour as sunspot number, peaking
between 8 d and 2 d before t = 0. The downward overall trends in these parameters results from this study using data from
the declining phase of the solar cycle. All three of these distributions appear towards the lower end of their percentile
ranges which is a consequence of a minority of triggers coming from the times of enhanced solar activity at the beginning
of the study period. We have chosen not to subtract a median value from each epoch of data before calculating the median
in these parameters to be consistent with the analysis of all the other parameters in which we are looking for a threshold
effect where absolute values are pertinent to their relative weighting.
Figure 2. The top panel contains the median total solar irradiance (TSI) measured around the times of the highspeed solar wind streams arriving at Earth. The middle panel contains the median response in sunspot number (SSN). The
third panel contains the median response in the Mg II emission.
4.3. Energetic particles at Earth
Figure 3 presents the response of high energy GCR and lower energy SEP fluxes to the arrival of fast solar wind
streams at Earth. The top panel presents the median daily change in cosmic ray flux at Earth, as measured by the Oulu
neutron counter. With the approach of the solar wind stream and its associated increase in magnetic shielding, the average
GCR flux decreases by 1.4% from around 141 570 counts to a minimum of 139 571 at t = 0. This minimum is
significantly outside the 95 and 99 percentiles of the dataset (the dashed and dotted lines, respectively). Before the
decrease, the count rates are higher than average (just above the 99 percentile) as was shown to be a persistent feature
ahead of CIR s (Rouillard and Lockwood 2007) and demonstrating that the interaction regions are significant depressors
of the overall average GCR flux. The decrease starts some 5–10 d before t = 0 and the subsequent recovery to pre-event
levels takes around 40 d. This is because the fast/slow solar wind interaction establishes a planar interaction front that is
wound into a spiral configuration. Because of the large gyroradius of GCRs in the heliosphere, this can deflect GCRs that
would have reached Earth even before it arrives at the Earth (at t < 0), but becomes a more effective shield as it passes
over Earth, giving the sudden decline in fluxes seen at t = 0. As the interaction front moves outward GCRs can diffuse
into its wake, giving the gradual recovery to pre-event levels that we observe.
Figure 3. Median response in galactic cosmic ray flux (top panel) as measured by the ground-based neutron monitor at
Oulu, Finland. The second, third and fourth panels present median proton flux measurements from the GOES satellite
dataset for three energy channels; >1 Mev (top), >30 Mev (middle) and > 100 Mev (lower). The median response in each
parameter is represented by a solid line, the standard error in this median as a grey area around the line while the dashed
lines and the dotted lines correspond to the 95% and 99% levels of the dataset respectively. These percentile levels were
calculated by repeating the analysis many times using random trigger times and determining the levels in each time bin
that contained 95 and 99% of the data points.
Associated with the CIRs are enhancements in SEPs. The lower panels presents a selection of energy channels
(>1 Mev, > 30 Mev, >100 Mev) measured by the GOES satellites (GOES N Databook 2006). These channels
demonstrate the evolution of SEP flux through the observed energy spectrum. There is a doubling in the median proton
flux in the lower energy channel (>1 MeV) for 10 d around t = 0, along with subsequent smaller enhancements 27 and 54
d later. Fluxes of protons with energies exceeding 30 Mev (third panel) reveal a 9% increase in particle flux in the 3 d
ahead of t = 0, dropping to a level 5% above the pre-trigger levels and decaying from this level over the subsequent 50 d.
The highest energy protons (>100 MeV) are once again enhanced over the pre-trigger levels by around 9% and remain
elevated for the subsequent 40 d, varying in intensity with a period of 18 d.
4.4. Lightning and thunder days
The top panel of figure 4 presents the median daily response in lightning rates as measured by the ATD system
of the UK Met Office. Since the meteorological conditions necessary to produce lightning are not always present, these
data are dominated by times for which there was little or no lightning. In order to calculate a meaningful median, these
zero values were not included in our calculations by requiring a minimum mean lightning rate of one stroke per hour.
This is not unreasonable since it is just recognition of the fact that convective instability must be present for lightning to
occur. This reduces the number of data points included in each time bin of the composite analysis to a mean value of
135 ± 2 (of 405 trigger events) with no bin containing fewer than 93 data points, ensuring that any median value is taken
from a distribution containing sufficient points that the median would not be influenced by outliers. There is a significant
enhancement in median lightning rates starting 10 d before t = 0 compared with median lightning rates from earlier times.
This enhanced lightning rate decays back to pre-event levels over the next 50 d. While the lightning rates remain
enhanced for many days, there is a variation of around 8 d within these enhanced values and a relatively low response
from t = 0 d to t = 5 d. The mean lightning rate for the 40 d before t = 0 is 321 ± 17 while the mean lightning rate for the
40 d after t = 0 is 422 ± 30. A spectral analysis of the daily ATD counts revealed no significant periodicities in the
original data.
Figure 4. The top panel contains the median daily lightning rate over the UK as measured by the arrival time
difference (ATD) system of the UK Met Office, during 2000–2005. The lower panel shows the median response in
thunder days recorded at all UK Met Stations scaled by the number of stations making manual measurements each day.
The median response in each parameter is represented by a solid line, the standard error in this median as a grey area
around the line while the dashed lines and the dotted lines correspond to the 95% and 99% levels of the dataset
respectively. These percentile levels were calculated by repeating the analysis many times using random trigger times and
determining the levels in each time bin that contained 95 and 99% of the data points.
Because operation of the lightning detection system depends on the propagation properties of the ionosphere,
which may also be influenced by the solar changes, we also consider a less sensitive but highly robust measure of
thunderstorms, manual acoustic detection of thunder on 'thunder days'. If thunder has been heard by an observer within a
24 h period, a value of 1 is recorded while the absence of thunder over the same period is recorded as 0. Such a binary
measurement contains less information than a count of lightning strokes. The advantage of using such data is that it does
provide an independent measure of the presence of thunder storms. Since a thunder day is a record of thunder being
heard, it is potentially susceptible to other noises, such as explosions or nearby traffic, being wrongly identified as
thunder. Such errors are likely to be localized and can be minimized by taking a median value across a number of stations
and by setting a threshold to ensure that the results are not dominated by the measurements where little or no lightning is
occurring. This threshold was set at 3% of the observed range of values to allow a similar number of (though not
necessarily the same) events on average to be recorded as was seen in the daily medians of ATD lightning data (top panel,
figure 4). The median fraction of stations on which thunder was heard at around 450 Met stations situated in marine and
land locations across the UK is shown in the second panel of figure 4. Since the number of manned stations is expected to
have varied throughout the interval being studied, thunder day counts were normalized by the number of stations known
to have made manual thunder day observations each day. The number of thunder days after t = 10 is clearly enhanced
compared with the number of thunder days prior to t = 10, with an encouraging agreement between the most significant
peaks (exceeding the 99th percentile) and the peak lightning rates seen in the ATD data. As the thunder day data
effectively records the presence of lightning with sufficient energy to generate audible thunder (Mackerras 1977), it
provides an independent measure compared with the radio detection of lightning rates used by the ATD system. The
mean fraction of stations recording thunder in the 40 d before t = 0 was 0.0424 ± 0.001 compared with 0.0445 ± 0.002 for
the 40 d after t = 0. The significance of the enhancements in lightning and thunder day rates was investigated by
conducting Kolmogorov−Smirnov tests on these distributions over 40 d before and after t = 0. This test determines
whether the two distributions represent subgroups from the same population or whether they come from statistically
distinct distributions. One additional advantage of this test is that it is independent of the shape of the event distribution
being investigated. For both the ATD data and the thunder day distributions, values in the 40 d after t = 0 were
significantly (to confidence levels >99.9%) different from the distributions of the same parameters in the 40 d before
t = 0. Using hourly triggers to identify responses in daily data can result in multiple-selection of response data in a given
time bin, effectively weighting the response by the longevity of the solar wind stream. Repeating the analysis for hourly
lightning data generates a similar, if noisier, response which passes the KS test at confidence levels far in excess of
99.9%. Such a reanalysis is not possible for the thunder data since it is a daily measurement. There is a sufficiently large
number of trigger times within the epoch under consideration that it is highly likely that a small number of lightning data
points corresponding to the same trigger time will appear in several time bins of the composite analysis. The top panel of
figure 1 shows that while most trigger times are assembled at time = 0, there are a small number of triggers distributed
throughout the composite time frame being considered. The fact that the lightning distributions before and after time = 0
pass the Kolmogorov−Smirnov test despite this cross-contamination of points strengthens the statistical significance of
this result.
Though the selection of solar wind triggers is independent of any seasonal changes at Earth, they could
nevertheless introduce a seasonal bias into the analysis of lightning data if they are not evenly distributed throughout the
year. Lightning rates increase dramatically in spring and decline rapidly in autumn. Any bias in the number of trigger
events between spring and autumn could therefore potentially introduce a bias throughout the 121 d time period of the
superposed epoch analysis. This is indeed the case for the above analysis, with more trigger events occurring in the spring
(132) than in the autumn (100) months. In order to investigate the possibility that the observed increase in lightning rates
was due to a seasonal bias, we repeated the analysis for triggers occurring during the summer months only and further
restricted the selection of triggers to ensure that only one trigger per day could contribute to the analysis. Given that the
width of the superposed epoch analysis window is of the order of four months, it would still be possible, despite the
restriction in trigger times, for data outside of the summer months to be convolved in the final result. In order to discount
this possibility, no data falling outside the summer months were used when calculating the median values in each daily
time bin in the restricted superposed epoch analysis. The results of this analysis are presented in figure 5. It can be seen
that the responses in both daily lightning and thunder day data are preserved and that the thunder day response is in fact
more pronounced. As before, these responses were tested using a Kolmolgorov−Smirnov test to see if the median values
for the 40 d either side of t = 0 were drawn from different distributions. Both passed at
99.9% (
0.1%
probabilities that these results occurred by chance). The mean values also passed a two sample T-test at 99.1% and
99.9% confidence levels (0.9%
0.1% that these results occurred by chance) for lightning and thunder data
respectively.
Figure 5. Median lightning rates (top panel) and thunder days (lower panel) in response to a restricted set of 36
solar wind trigger occurring during the months of June−August. In order that any seasonal bias does not influence the
median values in each time bin of the superposed epoch analysis, all data from times outside this strict seasonal window
were excluded before median values were calculated.
While these distributions were calculated from a much smaller number of triggers (32), the presence of lightning
during the summer months ensured that a high proportion of data in each time bin contained lightning (with a mean of
17.7 ± 0.3).
5. Discussion
Having determined that the arrival of fast solar wind streams at Earth is associated with a subsequent increase in
lightning rates, some possible mechanisms can be considered. Figures 4 and 5 present evidence that lightning and thunder
rates are enhanced following the passage of an interaction region over similar timescales to the observed depression in
GCR fluxes reaching Earth. This appears to contradict the results of earlier studies that have indicated an anti-correlation
between sunspots and thunder days (Pinto et al 2013). While sunspots themselves are merely a convenient proxy for solar
activity, the mechanism for the observed anti-correlation is thought to be through the modulation of the HMF throughout
the solar cycle. At sunspot maximum, the HMF is stronger, providing greater shielding from energetic GCRs at Earth.
With GCRs implicated in the triggering of lightning (Roussel-Dupré et al 2008; Gurevich and Zybin 2005), this provides
a mechanism by which sunspot number and thunder days would be anti-correlated over solar cycle timescales. In contrast,
our study, taken from the declining phase of a single solar cycle, considers the response in lightning rates to the arrival of
high-speed solar wind streams at Earth. These co-rotating solar wind streams are associated with a localized enhancement
of the HMF and a concomitant drop in GCR flux that ought to, at face value, have the same effect as solar cycle
variations. However the physics of these short timescale events is very different. The enhancement of the HMF is at the
fast/slow stream interface in the solar wind, resulting in a relatively small (though long-lived) ~2% decrease in GCR flux.
An explanation may be found in the enhancement of lower energy protons of solar origin measured in bands
between > 1 Mev and > 100 Mev also associated with these high-speed streams. For those channels with higher energies
(>30 Mev) these fluxes are enhanced to around 9% above pre-event levels for 40−50 d after t = 0. Of these, only higher
energy particles (>500 Mev) are capable of penetrating the atmosphere far enough to directly modulate atmospheric
conductivity in the lower atmosphere (e.g. Calisto et al 2012; Cliver 2006). The evolution in particle distribution seen in
the energy channels presented (particle fluxes starting earlier and remaining elevated for longer as the energy threshold
increases) is likely to continue beyond the highest detection threshold available on the GOES spacecraft. Furthermore,
these particles, being more localized and of lower energies that GCRs, can be significantly deflected by the Earth's
magnetic field, modulating their spectrum further. This could explain why the modulation of lightning rates begins before
the arrival of the high-speed stream at Earth and peaks between 12 and 18 d afterwards. Particles > 500 Mev have
sufficient energies to modulate the atmospheric conductivity above and within thunderclouds though they do not have
sufficient energy to be detected at ground level. If these particles are subsequently responsible for the observed
modulation in lightning rates it would explain why this result is in apparent contradiction to earlier studies which found
an anti-correlation between sunspot number and thunder days. Studies carried out on solar-cycle timescales will be
detecting the modulation of GCRs by the HMF. Enhancements of this field during times of high solar activity (large
sunspot number) will shield the Earth from GCRs, reducing the rate at which they could trigger lightning. In our study
however, the ~2% decrease in GCR flux is accompanied by a 9% increase in the flux of SEPs, the higher energy flux of
which could penetrate the atmosphere far enough to trigger lightning in the same way that GCRs are thought to do (e.g.
Gurevich and Karashtin 2013). Indeed, the sharpest drop in GCR flux around t = 0 is accompanied by a relative drop in
lightning rates, indicating that the total lightning rate is in fact a convolution of triggering by two distinct populations of
particles. While the exact mechanism by which this occurs is still unknown, this study demonstrates that solar wind and
atmospheric conditions on these small timescales are very different from the long-term average. It is perhaps not
surprising therefore that the response in lightning rates to co-rotating solar wind streams differs from that over a solar
cycle.
While a small 27 recurrence can be seen either side of t = 0 in the median response in GCR flux (top panel,
figure 3) no such recurrence is apparent in the lightning data (top panel, figure 4). While the arrival times of solar wind
streams at Earth can be determined with some precision (figure 1), the subsequent elevation of SEPs lasts for tens of days.
If this elevated particle flux is indeed responsible for the observed modulation of lightning rates, any 27 d recurrence
would be blurred out in the median values of elevated particle flux and lightning rate.
Some further inferences are possible from the upgrade of the ATD lightning detection system to ATDnet which
occurred in 2007 following our analysis period, which led to a much more sensitive lightning detection network for
meteorological purposes. The number of lightning strokes detected increased by an order of magnitude, preventing
continued detection of the solar wind effects observed between 2000 and 2005. This implies that, in the earlier period
considered here, it may have been the magnitude of individual lightning strokes that was increased. Such a shift would
bring more lightning strokes above the detection threshold of the ATD system and appear as an increase in the number of
strokes. The lack of response in later, more sensitive ATD data is also consistent with a change in the spectrum of
lightning magnitude. In the more recent ATD data the detection threshold is much lower, allowing a greater number of
smaller lightning strokes to be detected. Without any record of lighting stroke magnitude however, this cannot be tested
with the current dataset. A worthwhile future study would be to repeat this analysis using data from a global lightning
network such as the World Wide Lightning Location Network (Rodger et al 2005).
It is, however, unlikely that the relatively small changes observed in TSI, SSN and Mg II index (figure 2) could
in themselves explain the increased lightning rates through direct modulation of solar irradiance. Furthermore, if
irradiance effects were the origin of the changes observed, the much greater variability apparent in these parameters
throughout the eleven year solar activity cycle would be expected to modulate the lightning rates over a far greater range
than has been observed.
Clearly the existence of suitable weather conditions allowing thunderstorms to form is a pre-requisite for
modulation of lightning. The approximately 8 d periodicity seen in peak lightning rates after t = 0 is more comparable
with the timescales of weather systems than individual storms though the cause of such a period in our observations
remains unexplained. The data presented above does provide evidence that, if weather conditions are suitable to generate
active convection and electrified storms, lightning rates appear to be modulated by the SEPs associated with high-speed
solar wind streams. Since these high-speed streams co-rotate with the 27 d solar rotation, their arrival at Earth is
predictable in advance. This, coupled with an increasing understanding of energetic particle effects on the atmosphere,
makes it worthwhile pointing out the potential benefits to forecasting hazardous weather.
Acknowledgements
The authors would like to thank the UK Met Office for use of data from their ATD network and observing
stations which were made available via the British Atmospheric Data Centre, the Sodankyla Geophysical Observatory for
the use of the Oulu cosmic ray data (http://cosmicrays.oulu.fi), D J McComas (Southwest Research Institute) and N Ness
(Bartol Research Institute) for the use of ACE data which were made available via CDAweb
(http://cdaweb.gsfc.nasa.gov). The thunder day data were obtained from the Met Office Integrated Data Archiving
System (MIDAS) land and marine surface stations (1853-current), made available by the NCAS British Atmospheric
Data Centre.
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El Almanaque Náutico y el Astrónomo Aficionado
-
Carlos Gil, ACA
Introducción
Este artículo está dedicado a la astronomía de posición y constara de dos publicaciones, en el primero
se describe que es el Almanaque Náutico, como obtener el Tiempo Sideral (TS) y las coordenadas Horarias del
Sol (☼), la segunda parte, estará dirigida al uso y aplicación del resto de la información contenida en el mismo.
El Almanaque Náutico es una herramienta de ayuda para el navegante, pero que el astrónomo
aficionado puede hacer uso del mismo, conociendo como está diseñado y cuál es su contenido. Es editado por el
Departamento de Hidrografía dela de Marina de países con tradición náutica, tales como Alemania, Brasil,
China, Estados Unidos de Norte América, España, Francia, Italia, Japón, Noruega, entre otros, viene redactado
en el idioma oficial del país emisor.
En este artículo se asume la utilización del Almanaque Náutico 2.014, publicado por la Dirección de
Hidrografía y Navegación, y el Centro de Hidrografía de la Marina de Brasil bajo el No. DN 5 -70, el cual
puede ser obtenido de internet como un documento PDF. Al final de la descripción de este artículo se
encontraran extractos de dicho texto, elegidos para que se adecuen a los ejemplos presentados en este escrito.
Antes de seguir adelante e iniciar a describir el contenido y uso del material impreso en Almanaque
Náutico, se hace necesario revisar las definiciones relacionas con las Coordenadas Geográficas, Horizontales,
Horarias y Ecuatoriales, el Meridiano de Greenwich, el Meridiano del Punto del Equinoccio de Primavera o
Primer Puntos de Aries, el Tiempo Sideral, el Angulo Sideral, los Husos Horarios, la Hora Zonal y la Hora
Local, del lugar donde se realiza la observación o se determina la posición de un buque en el mar.
El Meridiano de Greenwich.Es
conocido
como meridiano
cero, meridiano
base o primer meridiano, es el meridiano a partir del cual se
miden las longitudes y se corresponde con la circunferencia
imaginaria que une los polos y recibe su nombre por pasar por la
localidad inglesa de Greenwich. El meridiano fue adoptado como
referencia en la conferencia internacional celebrada en 1884 en
Washington y definitivamente aceptadas por la Conferencia
Internacional de la Hora de Paris (1912)
Entre los acuerdos adoptados en la reunión de
Washington se destacan, la adopción de un único meridiano de
referencia, el meridiano que atraviesa el Observatorio de
Greenwich, será el meridiano inicial, las longitudes alrededor del
globo al este y al oeste se tomarán hasta los 180º, desde el
meridiano inicial, los días náuticos y astronómicos comenzaran a
la medianoche.
Coordenadas Geográficas.
La Tierra es considera como una esfera y
sobre ellas se definen los paralelos y meridianos.
Los meridianos son círculos máximos que pasan por
ambos polos y los paralelos son círculos que parten
de un máximo que ocurre en el ecuador y van
disminuyendo su longitud a medida que se acercan
a los polos
La latitud (Ø). Se cuenta a partir del
paralelo que divide la tierra en dos partes iguales,
denominado Ecuador, La latitud mide el ángulo
entre cualquier punto y ecuador. Las líneas de
latitud se denominan paralelos, es decir asumen
los valores que van desde el cero (0º) en el
ecuador, hasta los noventa grados (90º) en los
polos.
Longitud (λ).Se inicia a partir de un círculo máximo, denominado meridiano de referencia, al cual se le
asigna el valor cero grados (0º). La longitud mide el ángulo a lo largo del ecuador desde cualquier punto de la
Tierra. La longitud se cuenta en grados desde el meridiano de referencia (0º), hasta alcanzar el lado opuesto del
meridiano de referencia, es decir el meridiano ubicado a 180º, se establece que el Angulo medido de la longitud
hacia oeste se considera negativo y el medido hacia el este del meridiano de referencia es positivo.
Combinando estos dos ángulos, se puede expresar la posición de cualquier punto de la superficie de la
Tierra. Por ejemplo Puerto Cabello (Venezuela), tiene latitud 10º 28’ N, y longitud 68º 01’ W. Así un vector
dibujado desde el centro de la tierra al punto 10º 28’ grados norte del ecuador y 68º 01’ grados al oeste del
meridiano de referencia pasará por Puerto Cabello.
Tiempo Universal
El tiempo universal coordinado o UTC es el principal estándar de tiempo por el cual el mundo
regula los relojes y el tiempo. Es uno de los varios sucesores estrechamente relacionados con el tiempo medio
de Greenwich (GMT). Para la mayoría de los propósitos comunes, UTC es sinónimo de GMT, pero GMT ya no
es el estándar definido con más precisión para la comunidad científica.
La hora GMT se basa en la posición media del Sol y fue definida por primera vez a partir del mediodía
de Greenwich, pero el 1 de enero de 1.925, se adoptó la convención de que la jornada comenzase a la media
noche, atrasando aquel día 12 horas y desde entonces el GMT se sigue definiendo a partir de la medianoche de
Greenwich. Esta hora carece de cierta fiabilidad ya que se basa en el movimiento medio del Sol. Fue por esto por
lo que se definió la hora UTC, que tiene una gran precisión, ya que está dada por relojes atómicos.
Husos Horarios.En geografía, huso horario es cada una de las veinticuatro áreas en que se divide la Tierra, siguiendo
la misma definición de tiempo cronométrico, están centrados en meridianos de una longitud que es un múltiplo
de 15°, lo que implica que cubren 7,5º hacia el este u oeste del eje central del huso.
Anteriormente, se usaba el tiempo solar aparente, con lo que la diferencia de hora entre el tiempo
coordinado una ciudad y otra era de unos pocos minutos en el caso de que las ciudades comparadas que no se
encontraran sobre un mismo meridiano. El empleo de los husos horarios corrigió el problema parcialmente, al
sincronizar los relojes de una región al mismo tiempo solar medio.
Todos los husos horarios se definen en relación con el denominado tiempo universal coordinado (UTC),
huso horario centrado sobre el meridiano de Greenwich. Puesto que la Tierra gira de oeste a este, al pasar de un
huso horario a otro en dirección este hay que sumar una hora. Por el contrario, al pasar de este a oeste hay que
restar una hora. El meridiano de 180°, conocido como línea internacional de cambio de fecha, marca el cambio
de día.
Tiempo Sidéreo.
El tiempo sidéreo, también denominado tiempo sideral, es el
tiempo medido por el movimiento diurno aparente del equinoccio
vernal o punto de Aries, que se aproxima, aunque sin ser idéntico, al
movimiento de las estrellas. Se diferencia en la precesión del
equinoccio vernal con respecto a las estrellas. De forma más precisa, el
tiempo sidéreo se define como el ángulo horario del equinoccio vernal.
Cuando el equinoccio vernal culmina en el meridiano local, el tiempo
sidéreo local es 00.00
La figura de la izquierda, representa una proyección de la esfera
terrestre sobre el ecuador. En donde N representa el polo Norte, El
segmento Nϓ representa el meridiano del Punto de Aries y segmento
NG el meridiano de Greenwich.
El arco de circunferencia ϓG representa el valor del Angulo
Horario de Aries, medido con respecto al meridano de Greenwich, el
cual se cuenta en sentido del movimiento de las agujas
o en grados sexagesimales desde 0º hasta los 360º.
Tiempo sidéreo local (TSL) y Tiempo sidéreo de Greenwich
Los valores locales del tiempo sidéreo varían de acuerdo con la longitud del observador. Si nos movemos una
longitud de 15º hacia el este o hacia el oeste, el tiempo sidéreo aumenta o disminuye una hora sidérea.
El tiempo sidéreo de Greenwich es el Tiempo sidéreo local para un observador situado en el Meridiano de
Greenwich.
Coordenadas Horizontales.
Las coordenadas horizontales en lugar son:
A = Azimut y h = Altura.
El plano fundamental en este sistema de sobre la esfera
celeste es el plano horizontal astronómico local, o sea, un plano
paralelo al horizonte astronómico del lugar y que pasa por el centro
de la esfera.
El eje fundamental es la vertical astronómica del lugar, o
recta paralela a la vertical del lugar (hilo de la plomada) y que pasa
por el centro de la esfera celeste. Como sabemos esta corta a la
esfera en dos puntos: El Zenit astronómico Z y el nadir astronómico
Z’.
El Azimut(A)de un astro X, es por definición es el arco
del horizonte celeste comprendido entre el punto cardinal Sur S y el
punto X’, donde el circulo secundario, que pasa por el astro X, corta
al horizonte. Este círculo secundario que pasa por el Zenit y Nadir,
se le llama Círculo Vertical o simplemente vertical del astro. El
azimut se cuenta a partir del punto S en el sentido S-W-N-E, de 0º a
360º.
La Altura(h) de un astro X, es por definición, el arco X’X del circulo vertical del astro X, comprendido
entre X y el horizonte. Se cuenta a partir a partir del horizonte de 0 º y 90 º, positivamente hacia el zenit y
negativamente hacia el nadir. El círculo menor que pasa por el astro X y es paralelo al horizonte se llama
almicantarat.
Coordenadas Horarias.
En este sistema de coordenadas celestes, el plano fundamental es el ecuador celeste, que define como
eje fundamental el eje polar que pasa por los polos celestes norte, N, y sur S. Se llaman círculos horarios o
meridianos celestes los círculos secundarios que paran por los polos y paralelos celestes los círculos menores
paralelos al ecuador.
El ángulo horario (H)
en el sentido
retrogrado o sea W-N-E-S, en otras palabras en el
sentido de las agujas del reloj.
La declinación (δ) de un astro E, es por
definición, el arco XX del circulo horario que pasa por
el astro E, comprendido entre E y el ecuador. Se cuenta
a partir del ecuador de 0 º a 90 º, positivamente hacia
polo N y negativamente hacia el polo S.
Como consecuencia del movimiento diurno
respecto del lugar de observación, el astro recorre su
paralelo con movimiento uniforme, si prescindimos de
las pequeñas irregularidades de la rotación terrestre y de
las variaciones del polo, que son muy pequeñas en un intervalo de tiempo (una noche), resulta que: la
declinación δ es constante y el ángulo horario H varia proporcional con el tiempo. Este sistema de coordenadas,
depende del lugar del lugar del observador sobre la superficie de la tierra, llamándose por lo tanto coordenadas
locales.
En este sistema el movimiento diurno afecta solamente al ángulo horario H, mientras que la declinación δ,
permanece prácticamente invariable.
Coordenadas Ecuatoriales.
Este sistema de coordenadas celeste es independiente por completo de la posición del observador, siendo su
plano fundamental es el ecuador celeste y el eje fundamental es el eje polar.
La ascensión recta (α), es por definición, el arco de ecuador
comprendido entre los círculos horarios que pasan por el punto vernal ϓ
,
es decir en el sentido contrario al giro de las agujas del reloj.
La declinación (δ) de un astro, es por definición, el arco del
círculo horario que pasa por el astro, comprendido entre el astro y el
ecuador. Se cuenta a partir del ecuador de 0 º a 90 º, positivamente hacia
polo N y negativamente hacia el polo S.
En astronomía se denomina punto Aries o punto vernal al punto
de la eclíptica a partir del cual el Sol pasa del hemisferio sur terrestre al
hemisferio norte, lo que ocurre en el equinoccio de primavera sobre el 21
de marzo (iniciándose la primavera en el hemisferio norte y el otoño en el
hemisferio sur).
El punto Aries es el origen de la ascensión recta, y en dicho punto
tanto la ascensión como la declinación son nulas. Debido a la precesión de
los equinoccios este punto retrocede 50,290966” al año. Ahora el punto Ariesno se halla en la constelación
Aries (como cuando fue calculado por primera vez, hace por lo menos un par de miles de años) sino en su
vecina Piscis
Angulo horario sideral (SHA)
En los apartados anteriores se han mencionado las definiciones de los sistemas de coordenadas
utilizados por Los astrónomos y topógrafos, los cuales hacen uso de la ascensión recta (α) para determinar la
posición de un astro.
Los navegantes no utilizan la Ascensión Recta (α) y definen un nuevo ángulo para fijar la posición del
astro a observar, tomando como referencia el meridiano del Punto de Aries o Punto Vernal (ϓ).
Debido a que el meridiano de Greenwich gira con la Tierra de oeste a este, y en cambio, cada círculo
horario se mantiene fijo, manteniendo la posición prácticamente estacionaria correspondiente a cada astro en el
firmamento, es porque lo que los ángulos horarios, de todos los astros celestes aumentan aproximadamente 15º
por hora (360º en 24 horas), en contraste con las estrellas (15º2,46’/h), el ángulo horario en Greenwich, GHA del
Sol, la Luna y los planetas aumenta en fracciones ligeramente diferentes (y variables).
Este fenómeno se debe al giro de los planetas (incluida la propia Tierra) giran alrededor del Sol y en el
caso de la Luna, a su giro alrededor de la Tierra, introducen un movimiento aparente adicional de estos astros en
el firmamento. En muchos casos resulta adecuado medir la distancia angular entre el círculo horario de un astro
y el del punto de referencia sobre la esfera celeste, en vez de tomar como tal, al meridiano de Greenwich,porque
el ángulo así obtenido es independiente de la rotación de la Tierra.
El ángulo sidéreo (SHA), se define como la distancia angular de
un astro al círculo horario (meridiano superior) del primer punto de Aries
(Nϓ
El valor del ángulo horario del astro en Greenwich (GHA) del astro
(☼), resulta ser la suma de su SHA y el GHA Aries, que a su vez es el
GHA del primer punto de Aries:
GHA = SHA + GHA Aries (1)
La figura anterior nos relaciona en forma directa, la Ascensión
Recta del cuerpo celeste (☼), que se mide desde el meridiano del primer
punto de Aries o punto vernal (Nϓ), hasta el meridiano donde se localiza el
astro (N☼),quedando para completar una circunferencia el Angulo Sidéreo
del astro (☼), por lo cual tenemos que:
☼
] (2)
El símbolo ubicado entre el corche significa que la AR y SHA deben estar expresados en horas, si la
ascensión recta viene expresada en grados, dividimos el valor de la ascensión recta entre 15, recordando que 15 º
de arco, son equivalentes una hora de tiempo. Las formulas (1) y (2), nos permiten obtener el valor de la
ascensión recta o del SHA conociendo cualquier de ellos.
Que contiene un Almanaque Náutico?
Un Almanaque Náutico, es una publicación impresa o digitalizada, que contiene información
relacionadas con las efemérides del Punto de Aries, los planetas utilizados en la navegación, Estrellas, el Sol, la
Luna, los eclipses de sol y de luna, tablas de conversión de unidades tiempo en unidades de arcos e
instrucciones para el uso del mismo, así como otras informaciones relacionadas con el tópico de la navegación.
La información que se puede extraer del Almanaque Náutico, esta tabulada en referencia al Tiempo
Universal (TU) del meridiano de Greenwich y por lo tanto para hacer uso del Almanaque en cualquier
momento, se hace necesario conocer del Tiempo Universal (TUG) y la Fecha en Greenwich.
La información relacionada con el TUG, TSG y las Coordenadas Horarias las encontramos en El
Almanaque en las hojas denominadas Efemérides o también conocidas como las Hojas de Uso Diario, las
cuales presentan la siguiente información.
En la parte superior de las mismas, para las fechas correspondiente al año para el cual está editado
observamos, así por ejemplo, los días 1,2 y 3 del mes de Enero del 2.014se localizan en las páginas #12 y #13,
los días 4, 5 y 6 de Mayo del 2.014, en las páginas #94 y #95.
La página (#12) y sus similares, en su encabezamiento observamos la primera fila dedicada las fechas
correspondiente a los días 1,2 y 3 de Enero 2014, la segunda fila , se observan siete (7) columnas, que leídas de
izquierda a derecha, la primera se corresponde con el Tiempo Universal (TU), la segunda con el valor de
AHGϓ o Tiempo Sideral, de la tercera a la sexta columna, se localizan los planetas Venus, Martes, Júpiter y
Saturno, el número que aparee a la derecha del nombre de los planetas en estas columnas se corresponde con la
magnitud de brillo de cada uno de ellos para eses día en particular, la séptima columna esta dedicadas a las
estrellas más visibles para el navegante.
En la tercera fila, desde la segunda columna hasta sexta columna, están descritas las iniciales del
Angulo Horario en Greenwich (AHG) y la declinación (δ), de cada uno de los elementos mencionados en la
segunda fila. En la columna dedicada a las estrellas, encontramos el nombre de cada una de estas y las iniciales
del Angulo Sidéreo (ARV) y la declinación (δ). En la cuarta fila encontramos en la primera columna las iniciales
del día (d) y la hora (h), de la segunda columna a séptima columna observamos el valor de las unidades
utilizados para los valores dados expresadas en grado (º) y minutos (‘) de arco.
La columna del Punto de Aries (ϓ), nos da información sobre el Angulo Horario de este en Greenwich.
Su valor se obtiene entrando con la hora del tiempo universal (TU), expresada en unidades exactas de horas, las
cuales van desde las 0 horas hasta las 23horas, el valor obtenido del Angulo Horario del punto de Aries en
Greenwich (AHGϓ), vienen expresados en grados y minutos de arco.
Como las observaciones astronómicas no se realizan en unidades exactas de tiempo sino en fracciones
expresadas en horas, minutos y segundo, se hace necesario hacer uso de las “páginas amarillas”, las cuales
permiten convertir minutos y segundos de tiempo en unidades de arco equivalentes.
Las páginas amarillas muestran las tablas de interpolación (Acrésimos e Correςões), que permiten
convertir unidades de tiempo en unidades de arco. Están numeradas en forma consecutiva en la superior desde
los 0 minutos hasta los 59 minutos, cada una ella dividida en 60 segundo. La parte inferior de las mismas, están
numeradas desde la página II hasta la XXII. Se anexan la página XXV que contiene los minutos 46ᵐ y 47ᵐ
La segunda página (#13), correspondiente a los días 1,2y 3 de Enero 2.014, se observan siete (7)
columnas, que leídas de izquierda a derecha, muestran en la primera columna El Tiempo Universal y debajo de
ella se aprecia el número del día, en este caso corresponde al día primero (1) de Enero y las horas contadas desde
las 00 horas hasta las 23 horas.
La segunda columna presenta las coordenadas horarias del Sol, la tercera columna contiene los datos
referidos a la luna, las próximas ochos columnas están referidas a la latitud y los valores relacionados con el
crepúsculo náutico y civil, como también el orto y ocaso del sol y la luna. El uso de esta página será descrita en
el próximo articulo.
USO PRÁCTICO DEL ALMANAQUE NAUTICO.
Los ejemplos planteados para conocer el uso y manejo del Almanaque Náutico están referidos al uso de
las páginas #94 y #95, correspondientes a los días 4, 5 y 6 de Mayo del 2.014, estas se encuentran al final del
artículo. Dado que este almanaque náutico está escrito en el idioma portugués se hace necesario recordar que los
días de la semana se denominan en este idioma, Domingo (Domingo), lunes (segunda - feria), martes (terςa feria), miércoles (quarta - feria), jueves (quinta – feria), viernes (sexta - feria), Sábado (Sábado).
Ejemplo #1. Determinar el Angulo Horario del punto Vernal o Punto de Aries en Greenwich (AHGϓ),
a las 7 horas de tiempo universal (TU), del día lunes5 de mayo del 2.014.
Solución. Buscamos en las páginas de Uso Diario o de las Efemérides del Almanaque Náutico (pagina
#94), la fecha a la cual se desea conocer el Angulo Horario del Punto Vernal o Punto de Aries en Greenwich
(AHGϓ), en este caso, es el día 5 lunes (segunda – feria) de Mayo del 2.014.
Seleccionamos en la primera columna dedicada al TU en la fecha dada (día 5, que corresponde a la
Segunda Feria), nos desplazamos por la columna marcada con la hora, hasta localizar el valor de las 7 horas y
en la columna opuesta a su derecha leemos el valor correspondiente al ángulo horario en Greenwich, GAH =328
º04,7’.
Fecha
Lunes 04-05-2014
TU
7.00
horas
TU
H
m
S
Grados
Minutos
7
0.00
0.00
328
4.70
0.00
0.00
0
0.00
Del A. Náutico
A H G ϓ
Correcciones
Valor del AHGϓ a las 7 horas de TU del día lunes 5/05/14
AHGϓ
328
4.70
Ejercicio #2.- Determinar el Angulo Horario del punto Vernal o Punto de Aries en Greenwich
(AHGϓ), a las 17 horas, 46 minutos y 23 segundos de tiempo universal, del día domingo 4 de mayo del 2.014.
Solución. Procedemos como en el ejercicio #1, para la fecha del Domingo (Domingo) 4 de mayo,
localizando el valor del ángulo horario de ϓ en Greenwich, a las 17 horas, con un valor de 117º 30.2’.
Faltándonos complementar el valor de los 46 minutos y 23 segundos del Tiempo Universal dado, este
valor se localiza en las páginas de corrección (Acrésimos e Correςões), en este caso (46 ᵐ,es la numero XXV),
en la cual recorremos la columna de los segundos hasta encontrar el valor 23, y en la columna correspondiente a
ϓ leemos el valor de 11º 37,7’.El Angulo del Punto Vernal o de Aries en Greenwich a la hora solicitada del
Tiempo Universal, es la suma de los dos valores antes obtenidos, a continuación se muestra el esquema
tradicional de realizar este tipo de cálculo.
Fecha
Domingo 04-05-2014
TU
17.00
horas
46.00
minutos
23.00
segundos
Del A. Náutico
A H G ϓ
TU
H
m
S
Grados
Minutos
17
0.00
0.00
117.00
30.20
46.00
23.00
11.00
37.70
128.00
67.90
Correcciones
Valor del AHGϓ a las 17 horas, 46 minutos y 23 segundos de TU
del día domingo 4/05/14
129.00
7.90
Ejemplo #3. Calcular el Tiempo Universal local, para realizaruna observación en un lugar cuyas
coordenadas geográficas son latitud
46ᵐ 23ˢ y el valor del AHGϓ = 129º 7.9’.
Gds
min
Seg
Gds
(Ø) - Norte
8.00
15.00
0.00
8.2500
(λ) - Oeste
60.00
20.00
12.00
60.3367
Data
Coordenadas geográficas
Hrs
min
seg
HL
22.00
43.00
50.00
Fecha
05-05-14
H
min
Seg
Fecha
HL
22.00
45.00
50.00
05-05-14
(λ) - Oeste
4.00
1.00
21.00
TUG
26.00
46.00
71.00
24.00
0.00
0.00
TUG
2.00
46.00
TUG
2.00
47.00
Hrs
min
seg
4.00
1.00
21.00
Solución
06-05-14
Cambio de fecha, con
71.00
06-05-14
esta se accede al
Almanaque
Náutico.
11.00
06-05-14
Del Almanaque Náutico
Gds
Min
Seg
AHϒ
253.00
51.50
0.00
11.00
49.70
0.00
2.00
Corrección
47.00
11.00
AHGϒ
06-05-14
264.00
101.20
0.00
AHGϒ
06-05-14
265.00
41.20
0.00
Longitud (λ) - Oeste
60.00
20.20
0.00
AHLϒ
205.00
21.00
0.00
Hrs
Min
Seg
13.00
41.00
24.00
HLϒ (TSL)
05-05-14
05-05-14
06-05-14
Anexos.
A continuación se encuentran las páginas#12, #13, #94 y #95 del Almanaque Náutico correspondiente al año
2.014 y la página XXV de las correcciones.
-
-
El Fenómeno de El Niño Histórico en Venezuela
Marcos A. Peñaloza-Murillo [email protected]
Universidad de los Andes. Facultad de Ciencias. Departamento de Física. Mérida
El ritmo intermitente e incesante de la Naturaleza impone una variación cíclica de sus propiedades y de sus
manifestaciones. En particular, el aire y el agua que nuestro planeta contiene, tienen sus propios pasos, sus propios ciclos.
Las mareas, la lluvia, los huracanes, las sequías, las crecidas, las estaciones, los tornados, el invierno, el verano,
las inundaciones, las corrientes marinas, las nevadas, las tormentas de polvo, el viento, el calor, el frío, El Niño, La Niña,
etc., van y vienen, se alejan y
retornan, con diferentes lapsos
e
intensidades,
en
un
intercambio
intricado
y
complejo
de
energía,
movimiento y masa. Dentro
del limitado entorno de nuestro
más
cercano
ambiente,
podemos sentir o percibir
directa o indirectamente las
fases de eso ciclos. Los
pescadores peruanos del siglo
19, que venían notando y
comentando
sobre
una
contracorriente costera cálida
que baja de vez en cuando,
después de Navidad, hacia
Ecuador y Perú, y que
ahuyentan a las anchoas
porque se quedan sin alimento, obtenido, vía zooplancton y fitoplancton marino de aguas frías, nunca se imaginaron que
estaban ante una de las manifestaciones regionales de un viejo fenómeno climatológico de globales proporciones
conocido hoy día como El Niño – Oscilación Sur (ENOS). Los eventos meteorológicos extremos ocurridos en Venezuela
en las últimas décadas, han venido ocasionando apreciables impactos ambientales con la mayor consecuencia social,
económica y política jamás vista en toda su historia, debido a una creciente vulnerabilidad por grave deterioro de sus
estructuras socio-económicas. Por la naturaleza misma de su propia climatología tropical, Venezuela se caracteriza por
tener anualmente temporadas lluviosas (invierno) y una sola temporada seca (verano), las cuales han recibido
significativa atención y detallado estudio. Como consecuencia, tales eventos extremos (amenazas) son del tipo de
extraordinarias sequías y del tipo de abundantes precipitaciones, siendo estas últimas, generadoras de grandes
inundaciones y deslaves como los ocurridos recientemente en 1987 en Aragua, en 1999 en Vargas, en 2005 en Mérida y a
finales de 2010 en todo el país debido presumiblemente al fenómeno inverso: La Niña. Diversas han sido las causas que
se han propuesto para explicar el origen de estos eventos extremos y, entre ellas, ENOS ha sido una de ellas.
Considerando que ENOS es reconocido como un fenómeno natural recurrente de vieja data en la historia (no
producido por un presunto “cambio climático global” antropogénico como muchos creen), el interés por saber desde
cuándo se tienen noticias e información sobre su presencia y sus efectos en Venezuela, cobra crucial importancia en el
registro histórico de la variabilidad climática del país. En investigación inédita en realización en la Universidad de los
Andes (Mérida), hemos podido descubrir que al menos las grandes sequías que afligieron al país en los años de 1607-08,
1618, 1661, 1728, 1760, 1772, 1776-78, 1812, 1869, 1891, 1925-26, 1940-41 y 1957 se debieron a eventos El Niño que
ocurrieron en los siglos 17, 18, 19 y 20. En particular, los veranos de 1728, 1891 y 1925-26 fueron muy severos. En 1942,
después de El Niño de 1940-41, hubo grandes lluvias por lo que se presume un evento La Niña como causa. Se ve,
entonces, que estos eventos (Niño-Niña) no tienen nada de raro, contrario a lo que se ha afirmado en otra parte [El
Nacional, 30-12-2010 (opinión)]. Hace más de 4 años y medio, El Niño, como nunca antes, comenzaba a estar de boca en
boca de todos los venezolanos por la fuerte sequía que se comenzaba a sentir. Este último El Niño de 2010 pasará a la
historia del país como el más famoso de todos, por la gigantesca y descarada manipulación mediática que el sector oficial
hizo de él para echarle la culpa de la crisis del sistema eléctrico nacional. Aún peor es la engañosa y persistente
manipulación oficial según la cual El Niño es causado por el “cambio climático” producido por economías capitalistas
(¿incluyendo a China?); esto no es cierto. Se estima que en el pasado han ocurrido varios Mega-El Niño como el de 178993. Después de en un período de transición entre La Niña y El Niño, éste último ya está de regreso en 2014 con sus
efectos de sequía sobre Venezuela.
Resuelto el Problema del Lado Oculto de la Luna
Penn State University, Astrophisics Dept.
Cuando un navío espacial nos envió por primera vez imágenes del lado oculto de la Luna, se observó que
carecía de las regiones oscuras que llamamos Mares. ¿Por qué?
Imágenes
compuestas:
Izquierda – Lado
oculto de la Luna
tomada
con
el
Lunar
Reconnaissance
Orbiter en Junio de
2009. Nótese la
ausencia
de
grandes
áreas
oscuras.
Derecha:
Imagen compuesta
de la cara visible de
la Luna, en ella si
se observan las
grandes
áreas
oscuras que llamamos “Mares”.
Los Mares oscuros – grandes áreas planas de Basalto en el lado visible de la Luna – se les dice a veces El
hombre en la Luna. Nada como ellas existe al otro lado, pero ¿por qué existen en el lado visible y no en el otro? Un
atrofísico de la Universidad de Pensilvania, cree que tiene la respuesta. Piensa que la ausencia de Mares, la cual se debe a
la diferencia de grosor de la Corteza entre ambos hemisferios, es una consecuencia de cómo fue originalmente formada la
Luna. El investigador reportó sus resultados el 9 de Junio en Astrophysical Journal Letters.
La ausencia de Mares en el hemisferio oculto fue llamado: “El problema de las Tierras altas del Lado Oculto”, y
viene de 1959, cuando la sonda rusa Luna 3 transmitió las primeras imágenes. Los investigadores notaron de inmediato la
ausencia de “Mares” en el lado oculto.
Los investigadores de Penn State University buscaron en los orígenes de la Luna. Se cree que este objeto se
formó al inicio del Sistema Solar, cuando un objeto del tamaño de Marte impactó a la Tierra, los escombros de este
choque eventualmente formaron la Luna. Poco después del gran impacto la Tierra y la Luna estaban muy calientes, dicen
los investigadores, La Tierra y el objeto no solo se fundieron, partes de él se vaporizaron, creando un disco de rocas,
magma, y vapor alrededor de la Tierra.
La geometría fue similar a la de exoplanetas rocosos muy cercanos a sus estrellas. La Luna estaba 10 o 20 veces
más cercana a la Tierra que ahora, y rápidamente asumió la posición Tidal asegurada con la rotación. Desde ese momento
enseñó siempre la misma cara a la Tierra. El seguro Tidal es producto de la gravedad de ambos objetos. La rotación lunar
se frenó casi desde el mismo momento de la formación de la Luna
La Luna, al ser más pequeña se enfrió rápidamente. La Tierra estaba a 2.500º C y radiaba hacia la Luna, el lado
oculto así se enfrió más rápido, mientras el lado visible se mantuvo fundido, creando un gradiente de temperatura entre
ambos lados. Este gradiente térmico es importante en la formación de la corteza, en la Luna, esta es rica en Aluminio y
Calcio, elementos difíciles de vaporizar. Estos se condensaron en la atmósfera del lado frío, pues el lado visible era muy
caliente. Cientos de millones de años después, estos elementos se combinaron con Silicatos en el Manto lunar para formar
feldespatos Plagioclasicos, que eventualmente se movieron a la superficie para formar la corteza. El Lado Oculto tiene
más de estos minerales y es más gruesa.
La Luna ya se ha enfriado completamente y no hay nada derretido debajo de la superficie. Después de enfriarse
la corteza, grandes meteoroides impactaron con el lado visible de la Luna y la quebraron, liberando vastos lagos de lava
basáltica que formaron los “Mares” del hemisferio visible, creando las características que conocemos como la del
Hombre en la Luna
Sin embargo, cuando los grandes meteoritos impactaron el lado oculto, en la mayoría de los casos, la corteza era
muy gruesa, y ninguna lava basáltica fue liberada, creando un lado oculto con valles, cráteres, y tierras altas, pero casi
ningún “mar”
Murió Nuestro Querido Amigo y Compañero de Estrellas Alberto Ramos
Por: Jesús H. Otero A.
El Sábado 21 de Junio, a la 01:40 horas, dejo de existir físicamente nuestro querido amigo de tantas aventuras
astronómicas Alberto Ramos. Un hombre amigo como pocos, un padre ejemplar, un esposo amante y magnífico, con una
hermosa familia, con quienes
compartía é inculcaba su pasión
por la Astronomía.
Murió el día del Solsticio
de Verano, para quedar brillando
en nuestros corazones y recuerdos
mientras existamos.
Alberto,
te
fuiste
físicamente, pero estarás con
nosotros y en nuestros recuerdos
por siempre. Cada vez que demos
una charla; observemos un evento
astronómico;
hagamos
un
Astrocamp, Taller, o Seminario; o
simplemente conversemos sobre
astronomía, veamos fotografías, o
contemos anécdotas. No te
diremos adiós, solo hasta luego.
Prepáranos el camino entre las
estrellas, donde nos esperaras con
tu sonrisa y buen humor.
Seminario: Los Métodos de la Ciencia
Por: Jesús H. Otero A.
Un Seminario muy interesante llamado: Breve Historia de los Métodos de la Ciencia, fue dictado por el Dr. Iván
Machín en el Campamento Nora, en los Altos Mirandinos.
Fueron dos días muy intensos mentalmente, pero sentimos que el tiempo voló, por lo interesante del mismo.
Recorrimos la evolución
del Método Científico
desde los Griegos hasta
el Bosón de Higgs.
El grupo fue
pequeño,
pero
muy
selecto. Dos Ingenieros,
Un
Geógrafo,
Un
Músico, Tres estudiantes
de Geofísica, y Una
estudiante
de
Bachillerato.
Las
preguntas profundas, y el
Seminario excelente, y
no podía sr de otra
manera siendo dictado
por el Dr. Iván Machín.
En la noche
aprovechamos observar
el firmamento, y al
nublarse hicimos una
interesante charla sobre
el Cambio Climático.
Primera evidencia directa de la Inflación Cósmica
Astrofísicos dicen que este trabajo ofrece nuevas perspectivas sobre algunas de las preguntas más básicas: ¿Por
Qué existimos?, ¿Cómo empezó el Universo
De acuerdo a las teorías astronómicas, hace
unos 14 mil millones de años atrás, nuestro Universo
comenzó a existir en un evento extraordinario que
llamamos Big Bang. En las primeras millonésimas de
segundo, el Universo se expandió exponencialmente,
estirándose más allá de de la vista de nuestros
mejores telescopios. Hoy,
(Marzo 16, 2014),
investigadores de él BICEP2, en colaboración con el
Harvard-Smithsonian Center for Astrophysics,
anunciaron la primera evidencia directa de esta
Inflación Cósmica.
Sus datos también muestran las primeras
imágenes de Ondas Gravitacionales, o rupturas del
Espacio –Tiempo, descritas algunas veces como: “El
primer tremor del Big Bang”. Finalmente los datos
confirman la profunda conección entre la Mecánica
Quántica y la Relatividad General.
“Detectar estos signos es una de las más
importantes metas en la Cosmología actual. Mucho
trabajo de mucha gente ha llevado este punto”, dice
John Kovak, líder colaborador del BICEP2
Estos resultados vienen de observaciones
realizadas por el Telescopio BICEP2, del fondo de
microondas cósmicas. Un suave resplandor dejado
por el Big Bang. Pequeñas fluctuaciones de este resplandor proveen pistas sobre las condiciones del Universo temprano.
Por ejemplo, pequeñas diferencias de temperaturas a través del cielo, muestran que partes del Universo eran más densas,
y donde eventualmente se condensarían galaxias y cúmulos de galaxias.
Desde que la radiación de fondo de Microondas es una forma de luz, exhibe propiedades de la Luz, incluyendo la
polarización. En la Tierra, la luz es difuminada por la atmósfera y se polariza. En el espacio, la radiación de fondo
también es polarizada por átomos y electrones.
“Nuestro equipo busca un tipo especial de polarización llamado Modos B, los que representan un retorcimiento
en los patrones de polarización de la Luz antigua”, dice Jamie Bock, co líder del Caltech/JPL.
Las ondas gravitacionales comprimen el espacio mientras viajan, y esto produce un patrón distintivo en la
radiación de fondo cósmica. Las ondas gravitacionales comportamiento muy parecido a las ondas de luz y pueden mostrar
polarizaciones a la derecha o izquierda.
“El patrón de modo B curvado es una firma única de las ondas gravitacionales debido a su comportamiento. Esta
es la primera imagen directa del ondas gravitacionales a través del espacio primordial”, dice Chao Lin Kuo, co líder de
Standford/SLAC.
El equipo examinó escalas espaciales en el cielo en intervalos de entre 1º y 5º.. Para hacerlo viajaron al Polo Sur
a fin de tomar ventaja de su aire frío y estable. “El Polo Sur es lo más cerca que se puede estar del espacio sin salir de la
Tierra. Es uno de los lugares más secos y transparentes del planeta, perfecto para buscar Microondas del Big Bang”.
El equipo se impresionó al detectar signos de polarización del Modo B más intensos que lo que muchos
cosmólogos habían predicho. El equipo analizó sus datos durante 3 años a fin de descubrir cualquier error, también
consideraron si el polvo de nuestra galaxia podía producir los patrones observados, pero los datos sugieren que es muy
improbable.
“Esto era como buscar una aguja en un pajar, pero encontramos una palanca” dijo Clem Pryke de la Universidad
de Minesota.
Al preguntársele al teórico Avi Loeb, de la Universidad de Harvard sobre las implicaciones de este
descubrimiento dijo: “Este trabajo ofrece una nueva visión sobre algunas preguntas muy importantes como: ¿Por qué
existimos?, ¿Cómo comenzó el Universo? Estos resultados no solo son humo de un disparo de la Inflación, ellos también
nos dicen cuando empezó la Inflación y cuan poderosa fue.
Reporte Eclipse Total de Luna Abril 15, 2014.
Las siguientes observaciones fueron realizadas desde el sector Pozo de Rosas de los Altos mirandinos. Durante
la observación solo fue posible obtener los tiempos de dos de los contactos, puesto que la nubosidad impidió la
observación precisa del resto. Sin embrago, se realizo la toma de varias fotografías cuando las circunstancias así lo
permitieron.
Nº
1
2
3
Tabla de datos
P1
U1
No se
observo
diferencia.
1h 28m 14s
1h 28m 14s
Nublado
U2
Nublado
Max
U3
Parcialmente
nublado
3h 54m 34s
3h 54m 34s
3h 54m 34s
Nota: Los dos primeros observadores forman parte de SOVAFA.
Instrumentos:
- Telescopio reflector Bushnell 76mm.
- Cámara digital canon
- Cámara digital fujifilm
- Reloj Casio con HLV
Fotografías
Fotografías
U4
P2
No visible
Observador
Isabel Farinha
Airlene Lugo
María Lugo
Planeta Marte
A partir de esta fotografía, los observadores
concluyen que el numero de Danjon que presento la
luna fue de L2. Sin embrago, a simple vista,
aproximadamente en el punto máximo del eclipse,
parecía que dicho numero era L1 puesto que los
detalles eran poco visibles y parte de la luna parecía
no distinguirse del resto del cielo.
Reporte Eclipse Total de Luna, Abril 15, 2014.
Jesús H. Otero A. y otros
Un grupo de observadores de SOVAFA nos reunimos en las instalaciones del Caracas Sports Club a fin de observar el
Eclipse Total de Luna de Abril 15, 2014.
Al inicio de la observación las condiciones atmosféricas eran ideales, pero al acercarse la hora del inicio de la
totalidad las condiciones se hicieron menos favorables, para finalmente nublarse por completo justo después del inicio de
esta. Esta nubosidad nos impidió obtener el Número de Danjon, ya que este debe medirse en la mitad de la totalidad, y a
esta hora la Luna estaba totalmente oculta tras las nubes.
Los observadores solo pudieron observar desde el comienzo del Eclipse hasta la llegada de la Totalidad, luego de esto, la
Luna se ocultó para no volver a observarse más.
Félix León desde Vista Alegre tuvo más suerte que nosotros y logró unas buenas fotografías, pero a él también
se le nubló el cielo y no pudo observar el medio de la Totalidad.
Se realizaron mediciones de los tiempos de los contactos, pero el paso de estratos no nos permitió medir los contactos con
los cráteres y mares. Julio Veloso y Alfredo Castillo filmaron el evento hasta la llegada de la totalidad.
Tabla de Datos
Contacto 1
05h 58m 21s
05h 58m 32s
05h 58m 59s
05h 59m 00s
05h 59m 02s
Contacto 2
07h 06m 56s
07h 06m 59s
07h 07m 11s
07h 07m 12s
07h 07m 07s
Instrumento
Binocular 10 x 50
Telescopio Orión 5”
Telescopio 8”
Binocular 10 x 50
Telescopio Optron 3”
Observador
Jesús Otero
Marianna Mazzone
Daniel Amado/
Bettina Steinhold
Julio Veloso / Alfredo Castillo
Foto: Felix León
Las malas condiciones atmosféricas impidieron la observación de Anthony Higuera y Tamara de Higuera desde
Puerto Ordaz, Oliver López desde Cabudare, José L. Herrera desde la Boyera, así como la de otros observadores en todo
el país.