Astronomical Picture of the Day

Transcription

8/29/2011
Objetos del Universo
Curso “Introducción a las Ciencias de
la Tierra y el Espacio II”
Introducción a CTE II, Depto.de Astronomía,
Facultad de Ciencias, UDELAR
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Objetivos
• Reconocer las
distintas clases de
objetos
astronómicos.
• Adquirir nociones
acerca de las
dimensiones y
escalas de tiempo y
de distancia que
involucran a los
objetos
astronómicos.
• Dar un avance de los
temas que
desarrollaremos a lo
largo del curso.
Facultad de Ciencias
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Introducción
• Universo o Cosmos: es la totalidad de espacio, tiempo,
materia y energía.
• Astronomía: es el estudio del Universo. Requiere un cambio
profundo en nuestra visión del Cosmos, y considerar a la
materia en escalas nada familiares a nuestra experiencia
cotidiana.
• La “Conexión Cósmica”: La mayoría de los elementos
químicos que forman nuestros cuerpos fueron creados hace
unos miles de millones de años en los núcleos calientes de
estrellas que desaparecieron hace mucho tiempo.
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Nuestro lugar en el
Universo
(En sentido antihorario: ) La Tierra
es uno de los 8 planetas que orbitan
al Sol en nuestro Sistema Solar.
Nuestro Sistema Solar es uno más
entre los cien mil millones de
sistemas estelares que forman parte
de nuestra galaxia, la Vía Láctea.
Nuestra galaxia es una de las dos
galaxias mayores de un conjunto de
algunas decenas que forman el
Grupo Local. El Grupo Local se
encuentra cerca de los confines del
Supercúmulo Local (en Virgo). El
Supercúmulo Local es una pieza
más de de una intrincada y
compleja estructura a gran escala
formada por galaxias a través del
Universo.
(Fig. 1.1, The Cosmic Perspective)
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Nuestro lugar en el
Universo
(De abajo hacia
arriba:) Una
estación espacial (y astronautas),
la Tierra, el Sistema Solar, la
vecindad local de estrellas, la Vía
Láctea, y el cúmulo de galaxias
más cercano. Los números indican
el aumento sucesivo en la escala
de la imagen.
(Fig. 1.5, Astronomy Today)
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Tiempo y Distancia
• Las unidades de distancia utilizadas en
Astronomía se eligen de acuerdo a la escala de
los objetos:
– Unidad Astronómica (Sistema Solar)
– Año luz, PARSEC (pc) y sus múltiplos (Kpc, Mpc) para
distancias interestelares y de objetos extragalácticos.
• Ir más profundo en el espacio equivale a viajar
más atrás en el tiempo.
– Por ej., la estrella Sirio se encuentra a 8 años luz del
Sol. Luego, hoy nos está llegando la luz que partió de
la estrella hace 8 años.
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El Cielo Nocturno
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Constelaciones
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En una noche despejada podemos apreciar
unas 3000 estrellas a simple vista (unas 6000
contando ambos hemisferios).
Las culturas humanas tienen una tendencia
natural a ver patrones en el cielo y relacionar
objetos aún cuando no exista una conexión
física o verdadera entre ellos.
Las civilizaciones ancestrales agruparon las
estrellas más brillantes en configuraciones
llamadas constelaciones.
Algunas constelaciones sirvieron como guías
de navegación o como calendarios primitivos
para predecir el comienzo de las estaciones,
y saber cuando plantar o cosechar, etc.
Actualmente constituyen una forma
conveniente para los astrónomos de
especificar grandes regiones de cielo. La UAI
ha dividido al cielo en 88 constelaciones.
El método más simple para localizar estrellas
es especificar su constelación y luego
ordenarlas de acuerdo a su brillo (Ej. Alfa de
Orionis = Betelgeuse, Beta de orionis = Rigel).
(Fig. 1.6, Astronomy Today)
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La constelación del Centauro es visible solamente desde
latitudes tropicales y meridionales. Alfa Centauri es la estrella
más próxima al Sol, distando unos 4.4 años-luz ( Fig. 1.10, The
Cosmic Perspective).
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La Esfera Celeste
• Durante el transcurso de una noche las constelaciones
parecen moverse lentamente por el cielo de Este a
Oeste, manteniendo invariables las posiciones relativas
de las estrellas, como si las mismas estuvieran “fijas” a
una esfera inmensa que rodeara a la Tierra.
• Dicho movimiento aparente es resultado de la rotación
de la Tierra en torno a su eje.
• La Esfera Celeste es entonces un artificio útil para
describir las posiciones de los objetos astronómicos. La
misma se define como una esfera imaginaria, de radio
arbitrario, centrada en el Observador.
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Movimiento General Diurno
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Coordenadas Astronómicas
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La Esfera Celeste permite definir un sistema de coordenadas celestes para
mediciones precisas de la posición de los astros.
Como se trata de un sistema de coordenadas esféricas, podemos
describirlo como un análogo de las coordenadas terrestres más familiares
longitud y latitud utilizados para ubicar una localidad sobre la superficie
de la Tierra.
El análogo de la longitud es la Ascención Recta (R.A.), y el de la latitud es
la declinación (DEC). La primera coordenada se mide en unidades de
tiempo (horas), y la segunda en unidades de arco (grados).
Dado que la R.A. es relativa a la posición del Equinoccio Vernal (o de
Aries), las coordenadas celestes no permanecen inmutables sino que
varían lentamente debido a la precesión del eje de rotación terrestre.
En consecuencia, en los catálogos astrométricos se especifican las
coordenadas celestes para una época estándar convencional (por ej. El 1
de enero de 2000).
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El Teorema de la Latitud
• La latitud del lugar es
igual a la altura del Polo
Celeste visible
(Fig. 2.7, Fundamental Astronomy, 5 Ed.).
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La Eclíptica
El aspecto del cielo
nocturno cambia a
medida que la Tierra se
mueve en su órbita en
torno al Sol. Como ilustra
la figura, el hemisferio
nocturno de la Tierra ve
diferentes series de
constelaciones en
diferentes épocas del
año.
(Fig 1.12, Astronomy Today).
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El Sistema Solar
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Cometas
• Imágenes de núcleos
cometarios tomadas
desde sondas espaciales a
corta distancia:
– NASA/EPOXI: Hartley 2 ,
2010.
– ESA/Giotto: 1P/Halley,
1986.
– NASA/JPL/Deep Space 1:
19P/Borrelly, 2001.
– NASA/JPL/Stardust :
81P/Wild 2, 2004.
– NASA/JPL/Deep Impact:
9P/Tempel 1, 2005.
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Asteroides
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Ceres
– Visto por el Hubble Space Telescope (HST). Se ha
realzado el contraste para distinguir detalles
superficiales.
– Descubierto por Giuseppe Piazzi el 1 de enero de
1801.
– Designación MPC: 1 Ceres (clase MB)
– Radio Equatorial: 487.3 ± 1.8 km
– Radio Polar: 454.7 ± 1.6 km
– Masa: 9.43 ± 0.07×1020 kg
(0.00015 masas terrestres, 0.0128 masas lunares).
– Catalogado como “Planeta enano”.
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Itokawa
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–
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Visto por la sonda Hayabusa (2005).
Designación MPC: 25143 Itokawa (clase Apollo).
Descubierto en 1998 por LINEAR.
Elipsoide 535 × 294 × 209 m.
Las imágenes de Hayabusa revelaron una llamativa
carencia de cráteres de impacto y una superficie
bastante rugosa con rocas. La densidad es
demasiado baja para un cuerpo monolítico, de roca
sólida, por lo cual se considera una “pila de
escombros”. Podría tratarse de un binario de
contacto.
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Objetos Transneptunianos (TNOs)
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Nebulosas
The Orion Nebula (a) is a giant cloud of gas and dust in which new stars and planets are forming. It is
located about 1,500 light-years from Earth, which means the light recorded in the photograph took
about 1,500 years to reach us. Thus, we see it as it was about 1,500 years ago. Photograph (b) shows
the constellation Orion, with labels for several bright stars and the location of the Orion Nebula. The
Orion Nebula is faintly visible to the naked eye, and you can see some detail with a good pair of
binoculars. (Note: All stars are so far away that they appear as pinpoints of light. Brighter stars appear
larger in the photograph only because they are overexposed. The crosses on the bright stars are an
artifact of the telescope used to take the photo (The Cosmic Perspective).
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Composición del medio
interestelar
Gas y Partículas de
Polvo
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NASA Astronomical Picture of the Day
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M45: The Pleiades Star Cluster
Credit & Copyright: Robert Gendler
Perhaps the most famous star cluster on
the sky, the Pleiades can be seen without
binoculars from even the depths of a lightpolluted city. Also known as the Seven
Sisters and M45, the Pleiades is one of the
brightest and closest open clusters. The
Pleiades contains over 3000 stars, is about
400 light years away, and only 13 light
years across. Quite evident in the above
photograph are the blue reflection
nebulae that surround the brighter cluster
stars. Low mass, faint, brown dwarfs have
also been found in the Pleiades. (Editors'
note: The prominent diffraction spikes are
caused by the telescope itself and may be
either distracting or provide aesthetic
enhancement, depending on your point of
view.)
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Cúmulos Globulares
• Omega Centauri (NGC
5139)
– Tamaño aparente: 36 minutos
de arco
– Contiene millones de
estrellas.
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M16: Stars from Eagle's EGGs
Credit: J. Hester, P. Scowen (ASU), HST,
NASA
Newborn stars are forming in the Eagle
Nebula. This image, taken with the
Hubble Space Telescope in 1995, shows
evaporating gaseous globules (EGGs)
emerging from pillars of molecular
hydrogen gas and dust. The giant pillars
are light years in length and are so
dense that interior gas contracts
gravitationally to form stars. At each
pillars' end, the intense radiation of
bright young stars causes low density
material to boil away, leaving stellar
nurseries of dense EGGs exposed. The
Eagle Nebula, associated with the open
star cluster M16, lies about 7000 light
years away.
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Brown Sun Bubbling
Our Sun may look like all soft and fluffy, but
its not. Our Sun is an extremely large ball of
bubbling hot gas, mostly hydrogen gas. The
above picture was taken in a specific color
of light emitted by hydrogen gas called
Hydrogen-alpha. Granules cover the solar
photosphere surface like shag carpet,
interrupted by bright regions containing
dark sunspots. Visible at the left edge is a
solar prominence. Our Sun glows because it
is hot, but it is not on fire. Fire is the rapid
acquisition of oxygen, and there is very little
oxygen on the Sun. The energy source of
our Sun is the nuclear fusion of hydrogen
into helium deep within its core.
Astronomers are still working to
understand, however, why so few neutrinos
are measured from the Sun's core.
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A Sunspot Up Close
Credit : Vacuum Tower Telescope, NSO, NOAO
Why would a small part of the Sun appear
slightly dark? Visible above is a close-up
picture of a sunspot, a depression on the
Sun's face that is slightly cooler and less
luminous than the rest of the Sun. The
Sun's complex magnetic field creates this
cool region by inhibiting hot material from
entering the spot. Sunspots can be larger
than the Earth and typically last for only a
few days. This high-resolution picture also
shows clearly that the Sun's face is a
bubbling sea of separate cells of hot gas.
These cells are known as granules. A solar
granule is about 1000 kilometers across
and lasts about 10 minutes. After that,
many granules end up exploding.
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Galactic Collision in Cluster Abell
1185
Credit & Copyright: Jean-Charles Cuillandre (CFHT),
Hawaiian Starlight, CFHT
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Clusters of galaxies are sometimes packed
so tight that the galaxies that compose them
collide. A prominent example occurs on the
left of the above image of the rich cluster of
galaxies Abell 1185. There at least two
galaxies, cataloged as Arp 105 and dubbed
The Guitar for their familiar appearance, are
pulling each other apart gravitationally. Most
of Abell 1185's hundreds of galaxies are
elliptical galaxies, although spiral, lenticular,
and irregular galaxies are all clearly evident.
Many of the spots on the above image are
fully galaxies themselves containing billions
of stars, but some spots are foreground stars
in our own Milky Way Galaxy. Recent
observations of Abell 1185 have found
unusual globular clusters of stars that appear
to belong only to the galaxy cluster and not
to any individual galaxy. Abell 1185 spans
about one million light years and lies 400
million light years distant.
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Hot Gas and Dark Matter
Credit: Richard Mushotzky (GSFC/NASA),
ROSAT, ESA, NASA
Is the gravity of the galaxies seen in thiis
image high enough to contain the
glowing hot gas? Superposed on an
optical picture of a group of galaxies is an
image taken in X-ray light. This picture,
taken by ROSAT, shows confined hot gas
highlighted in false red color, and
provides clear evidence that the gravity
exerted in groups and clusters of galaxies
exceeds all the individual component
galaxies combined. The extra gravity is
attributed to dark matter, the nature and
abundance of which is one of the biggest
mysteries in astronomy today.
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Streams of Stars in the Virgo Cluster of
Galaxies
Credit: C. Mihos (CWRU) et al., KPNO, NOAO,
NSF
How do huge clusters of galaxies evolve? To
help find out, astronomers pointed the wideangle Burrell-Schmidt telescope on Kitt Peak
National Observatory in Arizona, USA at the
nearby Virgo Cluster of Galaxies. After
hundreds of 15-minute exposures taken over
two months in early 2004, the result is a
dramatically deep and wide angle image of
Virgo, the closest cluster of galaxies to our
Milky Way Galaxy. Bright foreground stars have
been digitally removed from the image but are
still represented by numerous unusual dark
spots. Inspection of the above image shows
unusually large halos for the brightest galaxies
as well as unusual faint streams of stars
connecting Virgo galaxies that previously
appeared unrelated
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NGC 1316: After Galaxies Collide
Credit: P. Goudfrooij (STScI), Hubble Heritage Team,
(STScI/AURA), ESA, NASA
How did this strange-looking galaxy form?
Astronomers turn detectives when trying to
figure out the cause of unusual jumbles of stars,
gas, and dust like NGC 1316. A preliminary
inspection indicates that NGC 1316 is an
enormous elliptical galaxy that includes dark
dust lanes usually found in a spiral. The above
image taken by the Hubble Space Telescope
shows details, however, that help in
reconstructing the history of this gigantic
jumble. Close inspection finds fewer low mass
globular clusters of stars toward NGC 1316's
center. Such an effect is expected in galaxies that
have undergone collisions or merging with other
galaxies in the past few billion years. After such
collisions, many star clusters would be
destroyed in the dense galactic center. The dark
knots and lanes of dust indicate that one or
more of the devoured galaxies were spiral
galaxies. NGC 1316 spans about 60,000 light
years and lies about 75 million light years away
toward the constellation of the Furnace.
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Spiral Galaxies in Collision
Credit: Debra Meloy Elmegreen (Vassar College)
et al., & the Hubble Heritage Team (AURA/
STScI/ NASA)
Billions of years from now, only one of
these two galaxies will remain. Until then,
spiral galaxies NGC 2207 and IC 2163 will
slowly pull each other apart, creating tides
of matter, sheets of shocked gas, lanes of
dark dust, bursts of star formation, and
streams of cast-away stars. Astronomers
predict that NGC 2207, the larger galaxy
on the left, will eventually incorporate IC
2163, the smaller galaxy on the right. In
the most recent encounter that peaked 40
million years ago, the smaller galaxy is
swinging around counter-clockwise, and is
now slightly behind the larger galaxy. The
space between stars is so vast that when
galaxies collide, the stars in them usually
do not collide.
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Elliptical Galaxy NGC 4881 in Coma
Credit: W. A. Baum (U. Washington), WFPC2,
HST, NASA
Elliptical galaxies are unlike spiral galaxies
and hence unlike our own Milky Way Galaxy.
The giant elliptical galaxy named NGC 4881
on the upper left lies at the edge of the giant
Coma Cluster of Galaxies. Elliptical galaxies
are ellipsoidal in shape, contain no spiral
arms, contain little interstellar gas or dust,
and are found mostly in rich clusters of
galaxies. Elliptical galaxies appear typically
yellow-red, as opposed to spirals which have
spiral arms that appear quite blue. Much
speculation continues on how each type of
galaxy can form, on whether ellipticals can
evolve from colliding spirals, or spirals can be
created from colliding ellipticals, or both.
Besides the spiral galaxy on the right, all
other images in this picture are of galaxies
that lie well behind the Coma Cluster.
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Elliptical Galaxy M87
Credit & Copyright: Canada-France-Hawaii
Telescope, J.-C. Cuillandre (CFHT), Coelum
Elliptical galaxy M87 is a type of galaxy that
looks much different than our own Milky
Way Galaxy. Even for an elliptical galaxy,
though, M87 is peculiar. M87 is much bigger
than an average galaxy, appears near the
center of a whole cluster of galaxies known
as the Virgo Cluster, and shows an unusually
high number of globular clusters. These
globular clusters are visible as faint spots
surrounding the bright center of M87. In
general, elliptical galaxies contain similar
numbers of stars as spiral galaxies, but are
ellipsoidal in shape (spirals are mostly flat),
have no spiral structure, and little gas and
dust. The above image of M87 was taken
recently by the Canada-France-Hawaii
Telescope on top of the dormant volcano
Mauna Kea in Hawaii, USA.
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M31: The Andromeda Galaxy
Credit & Copyright: Robert
Gendler(robgendlerastropixs.com)
Andromeda is the nearest major galaxy to
our own Milky Way Galaxy. Our Galaxy is
thought to look much like Andromeda.
Together these two galaxies dominate the
Local Group of galaxies. The diffuse light
from Andromeda is caused by the
hundreds of billions of stars that compose
it. The several distinct stars that surround
Andromeda's image are actually stars in
our Galaxy that are well in front of the
background object. Andromeda is
frequently referred to as M31 since it is
the 31st object on Messier's list of diffuse
sky objects. M31 is so distant it takes
about two million years for light to reach
us from there. Although visible without
aid, the above image of M31 is a digital
mosaic of 20 frames taken with a small
telescope.
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Neighboring Galaxy: The Large
Magellanic Cloud
Credit & Copyright: AURA/NOAO/NSF
The brightest galaxy visible from our own
Milky Way Galaxy is the Large Magellanic
Cloud (LMC). Visible predominantly from
Earth's Southern Hemisphere, the LMC is
the second closest galaxy, neighbor to the
Small Magellanic Cloud, and one of eleven
known dwarf galaxies that orbit our Milky
Way Galaxy. The LMC is an irregular galaxy
composed of a bar of older red stars,
clouds of younger blue stars, and a bright
red star forming region visible near the top
of the above image called the Tarantula
Nebula. The brightest supernova of
modern times, SN1987A, occurred in the
LMC.
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The Milky Way in Stars and Dust
Credit & Copyright: Serge Brunier
The disk of our Milky Way Galaxy is home to hot
nebulae, cold dust, and billions of stars. This disk
can be seen from a dark location on Earth as a
band of diffuse light across the sky. This band
crosses the sky in dramatic fashion in the above
series of wide angle sky exposures from Chile.
The deepness of the exposures also brings to
light a vast network of complex dust filaments.
Dust is so plentiful that it obscures our Galaxy's
center in visible light, hiding its true direction
until discovered by other means early last
century. The Galactic Center, though, is visible
above as the thickest part of the disk. The diffuse
glow comes from billions of older, fainter stars
like our Sun, which are typically much older than
the dust or any of the nebulae. One particularly
photogenic area of darkness is the Pipe Nebula
visible above the Galactic Center. Dark dust is not
the dark matter than dominates our Galaxy -that dark matter remains in a form yet unknown.
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The Milky Way in Infrared
Credit: E. L. Wright (UCLA), The COBE
Project, DIRBE, NASA
At night, from a dark location, part of the
clear sky looks milky. This unusual swath
of dim light is generally visible during any
month and from any location. Until the
invention of the telescope, nobody really
knew what the "Milky Way" was. About
300 years ago telescopes caused a
startling revelation: the Milky Way was
made of stars. Only 70 years ago, more
powerful telescopes brought the further
revelation that the Milky Way is only one
galaxy among many. Now telescopes in
space allow yet deeper understanding.
The above picture was taken by the COBE
satellite and shows the plane of our
Galaxy in infrared light. The thin disk of
our home spiral galaxy is clearly apparent,
with stars appearing white and interstellar
dust appearing red.
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M101: The Pinwheel Galaxy
Credit & Copyright: Jean-Charles
Cuillandre (CFHT), Hawaiian Starlight,
CFHT
Why do many galaxies appear as spirals? A
striking example is M101, shown above,
whose relatively close distance of about
22 million light years allow it to be studied
in some detail. Recent evidence indicates
that a close gravitational interaction with
a neighboring galaxy created waves of
high mass and condensed gas which
continue to orbit the galaxy center. These
waves compress existing gas and cause
star formation. One result is that M101,
also called the Pinwheel Galaxy, has
several extremely bright star-forming
regions (called HII regions) spread across
its spiral arms. M101 is so large that its
immense gravity distorts smaller nearby
galaxies.
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Imágenes de objetos del Universo
adquiridas desde el NASA/ESA HST
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The large Whirlpool Galaxy (left)
is known for its sharply defined
spiral arms. Their prominence
could be the result of the
Whirlpool's gravitational tug-ofwar with its smaller companion
galaxy (right).
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M81, a spiral galaxy similar to our
own Milky Way, is one of the
brightest galaxies that can be
seen from Earth. The spiral arms
wind all the way down into the
nucleus and are made up of
young, bluish, hot stars formed in
the past few million years, while
the central bulge contains older,
redder stars.
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The Majestic Sombrero Galaxy
(M104) A brilliant white core is
encircled by thick dust lanes in
this spiral galaxy, seen edge-on.
The galaxy is 50,000 light-years
across and 28 million light years
from Earth.
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NGC 1365: A Nearby Barred Spiral
Galaxy
Credit: FORS Team, 8.2-meter VLT Antu,
ESO
Many spiral galaxies have bars across their
centers. Even our own Milky Way Galaxy is
thought to have a bar, but perhaps not so
prominent as the one in NGC 1365, shown
above. The persistence and motion of the
bar imply relatively massive spiral arms.
The placements of bright young blue stars
and dark dust lanes also indicate a strong
rotating density wave of star formation.
NGC 1365 is a member of the Fornax
Cluster of Galaxies. Because NGC 1365 is
relatively nearby, simultaneous
measurements of its speed and distance
are possible, which help astronomers
estimate how fast our universe is
expanding.
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Andromeda Island Universe
The most distant object easily visible to the
unaided eye is M31, the great Andromeda
Galaxy some two million light-years away. But
without a telescope, even this immense spiral
galaxy - spanning over 200,000 light years appears as a faint, nebulous cloud in the
constellation Andromeda. In contrast, a bright
yellow nucleus, dark winding dust lanes,
gorgeous blue spiral arms and star clusters are
recorded in this stunning telescopic digital
mosaic with a cumulative exposure of over 90
hours. While even casual skygazers are now
inspired by the knowledge that there are many
distant galaxies like M31, astronomers seriously
debated this fundamental concept only 80 years
ago. Were these "spiral nebulae" simply
outlying components of our own Milky Way
Galaxy or were they instead "island universes" -distant systems of stars comparable to the Milky
Way itself? This question was central to the
famous Shapley-Curtis debate of 1920, which
was later resolved by observations of M31 in
favor of Andromeda, island universe.
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Molecular Cloud Barnard 68
Credit: FORS Team, 8.2-meter VLT Antu, ESO
Where did all the stars go? What used to be
considered a hole in the sky is now known to
astronomers as a dark molecular cloud. Here, a
high concentration of dust and molecular gas
absorb practically all the visible light emitted
from background stars. The eerily dark
surroundings help make the interiors of
molecular clouds some of the coldest and most
isolated places in the universe. One of the most
notable of these dark absorption nebulae is a
cloud toward the constellation Ophiuchus
known as Barnard 68, pictured above. That no
stars are visible in the center indicates that
Barnard 68 is relatively nearby, with
measurements placing it about 500 light-years
away and half a light-year across. It is not known
exactly how molecular clouds like Barnard 68
form, but it is known that these clouds are
themselves likely places for new stars to form. It
is possible to look right through the cloud in
infrared light.
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Snake in the Dark
Credit & Copyright: Gary Stevens
Dark nebulae snake across a gorgeous
expanse of stars in this wide-field view
toward the pronounceable constellation
Ophiuchus and the center of our Milky Way
Galaxy. In fact, the central S-shape seen here
is well known as the Snake Nebula. It is also
listed as Barnard 72 (B72), one of 182 dark
markings of the sky cataloged in the early
20th century by astronomer E. E. Barnard.
Unlike bright emission nebulae and star
clusters, Barnard's nebulae are interstellar
dark clouds of obscuring gas and dust. Their
shapes are visible in cosmic silhouette only
because they lie in the foreground along the
line of sight to rich star fields and glowing
stellar nurseries near the plane of our
Galaxy. Many of Barnard's dark nebulae are
themselves likely sites of future star
formation. Barnard 72 is a few light years
across and about 650 light years away.
45
•
The Horsehead Nebula
Credit & Copyright: Nigel Sharp (NOAO),
KPNO, AURA, NSF
One of the most identifiable nebulae in the
sky, the Horsehead Nebula in Orion, is part
of a large, dark, molecular cloud. Also
known as Barnard 33, the unusual shape
was first discovered on a photographic plate
in the late 1800s. The red glow originates
from hydrogen gas predominantly behind
the nebula, ionized by the nearby bright
star Sigma Orionis. The darkness of the
Horsehead is caused mostly by thick dust,
although the lower part of the Horsehead's
neck casts a shadow to the left. Streams of
gas leaving the nebula are funneled by a
strong magnetic field. Bright spots in the
Horsehead Nebula's base are young stars
just in the process of forming. Light takes
about 1500 years to reach us from the
Horsehead Nebula. The above image was
taken with the 0.9-meter telescope at Kitt
Peak National Observatory.
46
23
8/29/2011
•
IC 1396 H-Alpha Close-Up
Credit: Nick Wright (University College London),
IPHAS Collaboration
Clouds of glowing hydrogen gas mingle
ominously with dark dust lanes in this close-up
of IC 1396, an active star forming region some
2,000 light years away in the constellation
Cepheus. In this and other similar emission
nebulae, energetic ultraviolet light from a hot
young star strips electrons from the
surrounding hydrogen atoms. As the electrons
and atoms recombine they emit longer
wavelength, lower energy light in a well known
characteristic pattern of bright spectral lines. At
visible wavelengths, the strongest emission line
in this pattern is in the red part of the spectrum
and is known as "Hydrogen-alpha" or just Halpha. Part of IPHAS, a survey of H-alpha
emission in our Milky Way Galaxy, this image
spans about 20 light-years and highlights bright,
dense regions within IC 1396, likely sites where
massive new stars are born.
47
•
An Orion Deep Field
Adrift 1,500 light-years away in one of the night sky's
most recognizable constellations, the glowing Orion
Nebula and the dark Horsehead Nebula are
contrasting cosmic vistas. They both appear in this
stunning composite digital image assembled from
over 20 hours of data that includes exposures filtered
to record emission from hydrogen atoms. The view
reveals extensive nebulosities associated with the
giant Orion Molecular Cloud complex, itself hundreds
of light-years across. The magnificent emission region,
the Orion Nebula (aka M42), lies at the upper right of
the picture. Immediately to its left are a cluster of of
prominent bluish reflection nebulae sometimes called
the Running Man. The Horsehead nebula appears as a
dark cloud, a small silhouette notched against the
long red glow at the lower left. Alnitak is the
easternmost star in Orion's belt and is seen as the
brightest star to the left of the Horsehead. Below
Alnitak is the Flame Nebula, with clouds of bright
emission and dramatic dark dust lanes. Fainter
tendrils of glowing hydrogen gas are easily traced
throughout the region in this Orion deep field.
48
24
8/29/2011
•
M2-9: Wings of a Butterfly Nebula
Credit: B. Balick (U. Washington) et al.,
WFPC2, HST, NASA
Are stars better appreciated for their art after they
die? Actually, stars usually create their most artistic
displays as they die. In the case of low-mass stars
like our Sun and M2-9 pictured above, the stars
transform themselves from normal stars to white
dwarfs by casting off their outer gaseous envelopes.
The expended gas frequently forms an impressive
display called a planetary nebula that fades
gradually over thousand of years. M2-9, a butterfly
planetary nebula 2100 light-years away shown in
representative colors, has wings that tell a strange
but incomplete tale. In the center, two stars orbit
inside a gaseous disk 10 times the orbit of Pluto.
The expelled envelope of the dying star breaks out
from the disk creating the bipolar appearance.
Much remains unknown about the physical
processes that cause planetary nebulae.
49
•
The Planetary Nebula Show
Credit: Courtesy Adam Block (KPNO Visitor
Program), NOAO, NSF
What do the Owl, the Cat's Eye, the Ghost of
Jupiter, and Saturn have in common? They're all
planetary nebulae of course, glowing gaseous
shrouds shed by dying sun-like stars as they run
out of nuclear fuel. Beautiful to look at, the
symmetric, planet-like shapes of these cosmic
clouds, typically 1,000 times the size of our solar
system, evoke their popular names. Flipping
through digital pictures made by participants in
the Kitt Peak National Observatory Visitor
Center's Advanced Observing Program,
astronomer Adam Block created this delightful
animation. Ten different planetary nebula
images are presented, each registered on the
central star. In order, their catalog designations
are NGC 1535, NGC 3242 (Ghost of Jupiter), NGC
6543 (Cat's Eye), NGC 7009 (Saturn Nebula),
NGC 2438, NGC 6772, Abell 39, NGC 7139, NGC
6781, and M97 (Owl Nebula). This glorious final
phase in the life of a star lasts only about 10,000
years.
50
25
8/29/2011
•
NGC 6369: The Little Ghost Nebula
Credit: Hubble Heritage Team, NASA
This pretty planetary nebula, cataloged as NGC
6369, was discovered by 18th century astronomer
William Herschel as he used a telescope to explore
the constellation Ophiucus. Round and planetshaped, the nebula is also relatively faint and has
acquired the popular moniker of Little Ghost
Nebula. Planetary nebulae in general are not at all
related to planets, but instead are created at the
end of a sun-like star's life as its outer layers expand
into space while the star's core shrinks to become a
white dwarf. The transformed white dwarf star, seen
near the center, radiates strongly at ultraviolet
wavelengths and powers the expanding nebula's
glow. Surprisingly complex details and structures of
NGC 6369 are revealed in this delightful color image
composed from Hubble Space Telescope data. The
nebula's main ring structure is about a light-year
across and the glow from ionized oxygen, hydrogen,
and nitrogen atoms are colored blue, green, and red
respectively. Over 2,000 light-years away, the Little
Ghost Nebula offers a glimpse of the fate of our Sun,
which should produce its own pretty planetary
nebula only about 5 billion years from now.
51
• The Witch Head Nebula
Credit: G. Greaney
Double, double toil and trouble; Fire burn,
and cauldron bubble ... Maybe Macbeth
should have consulted the Witch Head
Nebula. This suggestively shaped reflection
nebula is associated with the bright star
Rigel in the constellation Orion. More
formally known as IC 2118, the Witch Head
Nebula glows primarily by light reflected
from Rigel. Rigel is located about one
photo-width off the image to the right. Fine
dust in the nebula reflects the light. The
blue color is caused not only by Rigel's blue
color but because the dust grains reflect
blue light more efficiently than red. The
same physical process causes Earth's
daytime sky to appear blue, although the
scatterers here are molecules of nitrogen
and oxygen. The nebula lies about 1000
light-years away.
52
26
8/29/2011
•
Reflection Nebula NGC 1435
Credit & Copyright: Yuugi Kitahara
Reflection nebulae reflect light from a
nearby star. Many small carbon grains in
the nebula reflect the light. The blue
color typical of reflection nebula is
caused by blue light being more
efficiently scattered by the carbon dust
than red light. The brightness of the
nebula is determined by the size and
density of the reflecting grains, and by
the color and brightness of the
neighboring star(s). NGC 1435, pictured
above, surrounds Merope (23 Tau), one
of the brightest stars in the Pleiades
(M45). The Pleiades nebulosity is
caused by a chance encounter between
an open cluster of stars and a molecular
cloud.
53
•
NGC 1999: Reflection Nebula in Orion
Credit: Hubble Heritage Team (STScI) and NASA
A dusty bright nebula contrasts dramatically with a
dusty dark nebula in this Hubble Space Telescope
image recorded shortly after December's orbital
servicing mission. The nebula, cataloged as NGC
1999, is a reflection nebula, which shines by
reflecting light from a nearby star. Unlike emission
nebulae, whose reddish glow comes from excited
atoms of gas, reflection nebulae have a bluish cast
as their interstellar dust grains preferentially
reflect blue starlight. While perhaps the most
famous reflection nebulae surround the bright
young stars of the Pleiades star cluster, NGC
1999's stellar illumination is provided by the
embedded variable star V380 Orionis, seen here
just left of center. Extending right of center, the
ominous dark nebula is actually a condensation of
cold molecular gas and dust so thick and dense
that it blocks light. From our perspective it lies in
front of the bright nebula, silhouetted against the
ghostly nebular glow. New stars will likely form
within the dark cloud, called a Bok globule, as selfgravity continues to compress its dense gas and
dust. Reflection nebula NGC 1999 lies about 1500
light-years away in the constellation Orion, just
south of Orion's well known emission nebula,
M42.
54
27
8/29/2011
•
Supernova Remnant and Shock Wave
Credit: Chandra: NASA / CXC / GSFC, U.Hwang et
al.; ROSAT: NASA/GSFC/S.Snowden et al.
•
A massive star ends life as a supernova, blasting
its outer layers back to interstellar space. The
spectacular death explosion is initiated by the
collapse of what has become an impossibly dense
stellar core. Pictured is the expanding supernova
remnant Puppis A - one of the brightest sources
in the x-ray sky. Now seen to be about 10 lightyears in diameter, light from the initial stellar
explosion first reached Earth a few thousand
years ago. Recorded by the Chandra
Observatory's x-ray cameras, the inset view
shows striking details of the strong shock wave
disrupting an interstellar cloud as the shock
sweeps through preexisting material. The larger
field ROSAT image also captures a pinpoint
source of x-rays near the remnant's center. The
source is a young neutron star, the remnant of
the collapsed stellar core kicked out by the
explosion and moving away at about 1,000
kilometers per second.
55
•
Crab Nebula Mosaic from HST
Image Credit: NASA, ESA, J. Hester, A. Loll (ASU)
Acknowledgement: Davide De Martin (Skyfactory)
The Crab Nebula is cataloged as M1, the first
object on Charles Messier's famous list of things
which are not comets. In fact, the cosmic Crab is
now known to be a supernova remnant, an
expanding cloud of debris from the death
explosion of a massive star. Light from that stellar
catastrophe was first witnessed by astronomers
on planet Earth in the year 1054. Composed of 24
exposures taken in October 1999, January 2000,
and December 2000, this Hubble Space Telescope
mosaic spans about twelve light years. Colors in
the intricate filaments trace the light emitted from
atoms of hydrogen, oxygen, and sulfur in the
debris cloud. The spooky blue interior glow is
emitted by high-energy electrons accelerated by
the Crab's central pulsar. One of the most exotic
objects known to modern astronomers, the pulsar
is a neutron star, the spinning remnant of the
collapsed stellar core. The Crab Nebula lies about
6,500 light-years away in the constellation Taurus.
56
28
8/29/2011
•
The Mysterious Rings of Supernova
1987A
Credit: (ESA/ STScI), HST, NASA
What's causing those odd rings in
supernova 1987A? In 1987, the
brightestsupernova in recent history
occurred in the Large Magellanic Clouds. At
the center of the picture is an object central
to the remains of the violent stellar
explosion. When the Hubble Space
Telescope was pointed at the supernova
remnant in 1994, however, the existence of
curious rings was confirmed. The origins of
these rings still remains a mystery.
Speculation into the cause of the rings
includes beamed jets emanating from a
dense star left over from the supernova,
and a superposition of two stellar winds
ionized by the supernova explosion.
57
•
Tycho's Supernova Remnant in Xray
Credit: ROSAT, MPE, NASA
How often do stars explode? By looking at
external galaxies, astronomers can guess that
these events, known as a supernovae, should
occur about once every 30 years in a typical
spiral galaxy like our MilkyWay. However, the
obscuring gas and dust in the disk of our
galaxy probably prevents us from seeing
many galactic supernovae -- making
observations of these events in our own
galaxy relatively rare. In fact, in 1572, the
revered Danish astronomer, Tycho Brahe,
witnessed one of the last to be seen. The
remnant of this explosion is still visible today
as the shockwave it generated continues to
expand into the gas and dust between the
stars.Above is an image of the X-rays emitted
by this shockwave made by a telescope
onboard the ROSAT spacecraft. The nebula is
known as Tycho's Supernova Remnant.
58
29
8/29/2011
•
A Quasar Portrait Gallery
Credit J. Bahcall (IAS, Princeton), M. Disney
(Univ. Wales), NASA
•
Quasars (QUASi-stellAR objects) lie near the
edge of the observable Universe. Discovered
in 1963, astronomers were astounded that
such objects could be visible across billions of
light-years, as this implies they must emit
prodigious amounts of energy. Where does
the energy come from? Many believe the
quasar's central engine is a giant black hole
fueled by tremendous amounts of infalling
gas, dust, and stars. This gallery of quasar
portraits from the Hubble Space Telescope
offers a look at their local neighborhoods: the
quasars themselves appear as the bright starlike objects with diffraction spikes. The
images in the center and right hand columns
reveal quasars associated with disrupted
colliding and merging galaxies which should
provide plenty of debris to feed a hungry
black hole.
59
•
Finding Dark Matter
Credit & Copyright: A. J. Benson (Caltech) et al.,
U. Durham, PPARC
Where is dark matter? Galaxies rotate and move
in clusters as if a tremendous amount of unseen
matter is present. But does dark matter exist in
the greater universe too -- and if so, where? The
answer can be found by comparing the
distribution of galaxies observed with numerical
simulations. This comparison became much
more accurate recently when over 100,000
galaxy observations from the 2-Degree Field
Galactic Redshift Survey were used. In the above
frame from a computer simulation of our
universe, a 300 million light-year slice shows
dark matter in gray and galaxies as colored
circles. The red box indicates the location of a
rich cluster of galaxies, while the green box
shows a more typical cross-section of our
universe. Analyses indicate that the immense
gravity of the pervasive dark matter pulls normal
matter to it, so that light matter and dark matter
actually cluster together.
60
30
8/29/2011
•
Dark Matter Map
Credit: J.-P. Kneib (Observatoire MidiPyrenees, Caltech) et al., ESA, NASA
The total mass within giant galaxy cluster
CL0025+1654, about 4.5 billion light-years
away, produces a cosmic gravitational lens -bending light as predicted by Einstein's
theory of gravity and forming detectable
images of even more distant background
galaxies. Of course, the total cluster mass is
the sum of the galaxies themselves, seen as
ordinary luminous matter, plus the cluster's
invisible dark matter whose nature remains
unknown. But by analyzing the distribution
of luminous matter and the properties of
the gravitational lensing due to total cluster
mass, researchers have solved the problem
of tracing the dark matter layout. Their
resulting map shows the otherwise invisible
dark matter in blue, and the positions of the
cluster galaxies in yellow. The work, based
on extensive Hubble Space Telescope
observations, reveals that the cluster's dark
matter is not evenly distributed, but follows
the clumps of luminous matter closely.
61
•
WMAP Resolves the Universe
Credit: WMAP Science Team, NASA
Analyses of a new high-resolution map of
microwave light emitted only 380,000 years
after the Big Bang appear to define our
universe more precisely than ever before.
The eagerly awaited results announced last
year from the orbiting Wilkinson Microwave
Anisotropy Probe resolve several longstanding disagreements in cosmology
rooted in less precise data. Specifically,
present analyses of above WMAP all-sky
image indicate that the universe is 13.7
billion years old (accurate to 1 percent),
composed of 73 percent dark energy, 23
percent cold dark matter, and only 4
percent atoms, is currently expanding at the
rate of 71 km/sec/Mpc (accurate to 5
percent), underwent episodes of rapid
expansion called inflation, and will expand
forever. Astronomers will likely research the
foundations and implications of these
results for years to come.
62
31
8/29/2011
•
Welcome to Planet Earth
Credit: Apollo 17 Crew, NASA
Welcome to Planet Earth, the third
planet from a star named the Sun. The
Earth is shaped like a sphere and
composed mostly of rock. Over 70
percent of the Earth's surface is water.
The planet has a relatively thin
atmosphere composed mostly of
nitrogen and oxygen. Earth has a single
large Moon that is about 1/4 of its
diameter and, from the planet's
surface, is seen to have almost exactly
the same angular size as the Sun. With
its abundance of liquid water, Earth
supports a large variety of life forms,
including potentially intelligent species
such as dolphins and humans. Please
enjoy your stay on Planet Earth.
63
•
Earth at Night
Credit: C. Mayhew & R. Simmon
(NASA/GSFC), NOAA/ NGDC, DMSP Digital
Archive
This is what the Earth looks like at night.
Can you find your favorite country or city?
Surprisingly, city lights make this task
quite possible. Human-made lights
highlight particularly developed or
populated areas of the Earth's surface,
including the seaboards of Europe, the
eastern United States, and Japan. Many
large cities are located near rivers or
oceans so that they can exchange goods
cheaply by boat. Particularly dark areas
include the central parts of South
America, Africa, Asia, and Australia. The
above image is actually a composite of
hundreds of pictures made by the orbiting
DMSP satellites.
64
32
8/29/2011
• Water World
Credit: STS-45 Crew, NASA
Water (Dihydrogen Oxide, H2O) is a
truly remarkable chemical
compound, fundamental to life on
Earth. Earth is the only planet in
the Solar System where the present
surface temperature and pressure
allow the three forms of water,
solid (ice), liquid (ocean), and gas
(water vapor condensing in clouds)
to exist simultaneously. Water in
one of these forms accounts for
everything visible in this view of
Earth from space looking north at
the Bering Sea and the coast of
Alaska, USA, around Bristol Bay.
65
•
The Dust and Ion Tails of Comet
Hale-Bopp
Credit & Copyright: John Gleason (Celestial
Images)
In 1997, Comet Hale-Bopp's intrinsic
brightness exceeded any comet since 1811.
Since it peaked on the other side of the
Earth's orbit, however, the comet appeared
only brighter than any comet in two
decades. Visible above are the two tails shed
by Comet Hale-Bopp. The blue ion tail is
composed of ionized gas molecules, of which
carbon monoxide particularly glows blue
when reacquiring electrons. This tail is
created by the particles from the fast solar
wind interacting with gas from the comet's
head. The blue ion tail points directly away
from the Sun. The light colored dust tail is
created by bits of grit that have come off the
comet's nucleus and are being pushed away
by the pressure of light from the Sun. This
tail points nearly away from the Sun. The
above photograph was taken in March 1997.
66
33
8/29/2011
•
Ida and Dactyl: Asteroid and Moon
Credit: Galileo Project, JPL, NASA
•
This asteroid has a moon! The robot
spacecraft Galileo destined to explore the
Jovian system, encountered and
photographed two asteroids during its long
interplanetary voyage to Jupiter. The
second asteroid it photographed, Ida, was
discovered to have a moon which appears
as a small dot to the right of Ida in this
image from 1993. The tiny moon, named
Dactyl, is about one mile across, while the
potato shaped Ida measures about 36
miles long and 14 miles wide. Dactyl is the
first moon of an asteroid ever discovered.
The names Ida and Dactyl are from Greek
mythology. Many other asteroids are now
known to have moons.
67
• Asteroids in the Distance
Credit: R. Evans & K. Stapelfeldt (JPL), WFPC2, HST, NASA
Rocks from space hit Earth every day. The larger the
rock, though, the less often Earth is struck. Many
kilograms of space dust pitter to Earth daily. Larger bits
appear initially as a bright meteor. Baseball-sized rocks
and ice-balls streak through our atmosphere daily, most
evaporating quickly to nothing. Significant threats do
exist for rocks near 100 meters in diameter, which strike
the Earth roughly every 1000 years. An object this size
could cause significant tsunamis were it to strike an
ocean, potentially devastating even distant shores. A
collision with a Massive asteroid, over 1 km across, is
more rare, occurring typically millions of years apart, but
could have truly global consequences. Many asteroids
remain undiscovered. In fact, one was discovered in 1998
as the long blue streak in the above archival image taken
by the Hubble Space Telescope. In 2002 June, the small
100-meter asteroid 2002 MN was discovered only after it
whizzed by the Earth, passing well within the orbit of the
Moon. 2002 MN passed closer than any asteroid since
1994 XM1, but not as close as 2004 MN4 will pass in
2029. A collision with a large asteroid would not affect
Earth's orbit so much as raise dust that would affect
Earth's climate. One likely result is a global extinction of
many species of life, possibly dwarfing the ongoing
extinction occurring now.
68
34

Astronomical Picture of the Day

Transcription

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