The Construction and Use of the Astrolabe A Workshop

The Construction and Use of the Astrolabe
A Workshop (September, 21, 2012)
BYU Museum of Art
Glen M. Cooper
In connection with the Beauty and Belief exhibit
(Astrolabe templates and some diagrams adapted from: Timothy Mitchell:
http://www.astrolabeproject.com)
Assembly Instructions
Print out Front, Back, and Alidade/Rule pages on paper. Cut these out. Cut out
posterboard or heavy paper backing in the shape of the astrolabe. Glue front and back to
this posterboard sheet. Cut out alidade and double rule, and glue to posterboard. (Ignore
the single rule).
Print out Rete page on transparency sheet. Cut this out along the outer circular edge
ONLY.
Carefully drill/poke holes in the center of the astrolabe body, the center of the rete, and
the centers of the alidade and the double rule.
Attach the parts together with the nut and bolt that I’ll provide. The rete goes over the
front, and the double rule goes on top of the rete. The Alidade goes on the back.
Front
XI
XII
I
II
X
I
40
VI
II
I
II
X
V
VII
I
III
60
VI
VI
60
40
20
V
VII
I
III
VI
II
X
II
I
I
40° 14’
X
II
XI
XII
I
Back
90 90
80
70
er
Canc
20
60
30
30
50
6
7
5
M
ay
30
eo
20
20
8
4
Ta
u
10
10
3
Au
gu
st
30
20
30
30
9
30
10
L
60
10
40
20
10
s
ru
40
70
Gemi
ni
June
July
20
10
20
20
30
10
50
80
30
10
20
2
30
1
1
20
10
Virgo
September 0
30
20
30
32
28
24
er
20
tob
Oc
20
20
Umbra Versa
10
Libra
10
30
18
16
14
10
30
20
icorn
Capr
10
20
a s tr o l a b e. w y m a r c. c o m m e f e c it
30
December
30
Sc
o
20
10
30
Sagitt
arius
20
10
10
2
10
2
10
io
rp
y
uar
Jan
3
2
20
1
s
iu
ar
No 0
v
e
mb
er
1
20
6
5
4
Aq
u
2
10
7
7
3
30
8
9
8
30
30
9
4
10
10
5
1
10
20
11
10
Provo, Utah
Longitude: 111° 39’W
Time correction: 26 Minutes 37 Seconds
Glen
6
20
Fe
b
rua
ry
12
5
Pisce
s
14
Umbra Recta
5
30
10
16
Umbra Recta
10
20
March
5
10
10
10
11
Aries
10
20
20
20
ril
Ap
10
18
Umbra Versa
21
5
Sirius
Rigel
n
cyo
Pro
Bellatrix
Ald
ebar
20
20
10
Cancer
10
o
Le
20
an
10
Gemini
20
Tau 10
rus
Capella
m
Ha
al
20
ies
Ar
10
Alpheratz
20
Mark
ab
10
Pisces
Spic
20
10
Aqu
ariu 10
s
20
rpio
Sco
20
10
Diphda
20
Libra
rus
ctu
Ar
a
ec
ph
Rosalhague
air
a
ard
iph
Al
us
gul
Re
10
Vi
rg
o
Alioth
n
De
eb
Al
Vega
Alt
20
orn
pric
Ca
Sagi
ttar
ius
10
10
20
ares
Ant
Rete
Alidade
50
40
30
20
10
0
−10
−20
−10
−20
Double Rule
Use this double rule
Use this double rule
50
40
30
20
10
0
Single Rule
Do not use this single rule
Do not use the single rule
Major Components of the Astrolabe
Notes:
-The Alidade Rete and Rule are all designed to rotate freely.
-The Plates (also known as climates) of an astrolabe are specific to a given latitude.
Therefore most astrolabes contained a set of climates, that could be swapped out as
the user moved to different locations.
-The Astrolabe rule could be either single or double ended.
**DON'T LEARN THIS DIAGRAM**
11
The Front of the Astrolabe
S
Zenith
Time Markings
Horizon
E
W
Meridian
Twilight Line
Celestial North (Polaris)
N
Tropic of Cancer
Equator
Tropic of Capricorn
12
**LEARN THIS**
The Rete
Ecliptic - Path of the Sun
- Divided by Zodiac
(Sun moves counter-clockwise)
Winter Solstice
Polaris
Fall Equinox
Spring Equinox
Summer Solstice
Major Stars
**LEARN THIS**
18
Astrolabe Use Instructions
To determine solar longitude:
1. Determine the day of interest (e.g. Jan 15)
2. On the back of the astrolabe, find Jan 15 on the calendar circle.
3. Turn the rule to line up with Jan 15.
4. Read the solar longitude from the ecliptic (or Zodiac) circle (Capricorn 25°)
To determine the Ascendant (= “the Sign and degree rising over the horizon at a
given moment”):
1. Determine the day and time of interest (e.g. 3 PM Jun 15)
2. Determine the solar longitude for Jun 15 (Gemini 24°)
3. On the front of the astrolabe, turn the rule to the time of interest (here, 3 PM), and
hold it there with one finger.
4. With the rest of your hand, turn the rete so that the sun (i.e. Gemini 24°) lines up
with the rule and the time.
5. Look at the eastern horizon (on your left), and read the Sign and degree crossing
the horizon that that moment. (Scorpio 1°) That is the Ascendant.
To determine the Midheaven (= “the Sign and degree crossing the Meridian at a
given moment):
1. Follow steps 1-4 as for the Ascendant.
2. Look at the meridian, and read the Sign and degree that is crossing that that time.
(Leo 24°). That is the Midheaven.
To determine time of sunrise:
1. Determine the day of interest (e.g. Jun 15)
2. Determine the solar longitude for Jun 15 (Gemini 24°)
3. On the front of the astrolabe, align Gemini 24° with the eastern horizon (on the
left side)
4. Align the rule with the sun and horizon, and read the time of sunrise from the
outer circle. (4:35 AM)
To determine time of sunset:
1. Determine the day of interest (e.g. Jun 15)
2. Determine the solar longitude for Jun 15 (Gemini 24°)
3. On the front of the astrolabe, align Gemini 24° with the western horizon (on the
right side)
4. Align the rule with the sun and horizon, and read the time of sunset from the
outer circle. (7:30 PM)
To determine the time (day):
1. measure the sun’s altitude
2. find solar longitude for the current day on the back (e.g. Lib 25°)
3. Find this point on the zodiac circle on the front of the astrolabe
4. Line this point up with the altitude coordinate line on the front of the astrolabe
5. Align the rule with these two points, and read the time from the outer circle. This
is the solar time for the moment in question.
6. To convert to clock time, add an hour (if DST is in effect); add the equation of
time, and add the time zone correction. The result is clock time for your time
zone.
To determine the time (night):
1. measure the altitude of a star on the rete
2. find solar longitude for the current day on the back (e.g. Lib 25°)
3. Find this point on the zodiac circle on the front
4. Line the star up with the altitude coordinate on the front
5. Align the rule with the sun’s position on the zodiac circle, and read the time from
the outer circle. This is the solar time at night.
6. To convert to clock time, add an hour (if DST is in effect); add the equation of
time, and add the time zone correction. The result is clock time for your time
zone.
Bibliography
Chaucer, Geoffrey, A Treatise on the Astrolabe, addressed to his son, Lowys, A.D. 1391,
edited by Walter Skeat, London (1872). (available online –Google Books)
Gibbs, Sharon, and George Saliba. Planispheric Astrolabes from the National Museum of
American History. Vol. 45, Smithsonian Studies in History and Technology.
Washington, D. C.: Smithsonian Institution Press, 1984.
Grant, Edward, A Sourcebook in Medieval Science, Harvard University Press(1974)
Hand, Robert. The Astrolabe World Ephemeris: 2001-2050 at Midnight, Schiffer
Publishing (2000)
Hartner, W., ed. The Principle and Use of the Astrolabe. Edited by Arthur Upham Pope.
Vol. III, A Survey of Persian Art. London and New York: Oxford Univ. Pr., 1939.
Jamieson, Laura and Montero, Maria, Stereographic Projection, Chaucer and the
Astrolabe: http://www.math.ubc.ca/~cass/courses/m30901a/montero/math309project.html
King, David A. "The Origin of the Astrolabe according to the Medieval Islamic Sources."
Journal for the History of Arabic Science 5, no. 1-2 (1981): 43-83.
King, David A. “A Survey of Medieval Islamic Shadow Schemes for Simple TimeReckoning.” Oriens, Vol. 32 (1990), pp. 191-249
King, David A. Astrolabes from Medieval Europe, Variorum Collected Studies. Farnham,
Surrey, UK: Ashgate, 2011.
Michel, Henri, Traite de L’Astrolabe, Librarie Alain Brieux, Paris (1976). English
translation by James E. Morrison (1993) currently unpublished.
Morrison, James. The Astrolabe, Janus, 2007
Neugebauer, O. "The Early History of the Astrolabe." Isis 40, no. 3 (1949): 240-56.
Stoeffler, Johannes, Elucidatio Fabriquae Ususque Astrolabii, Oppenheim (1523).
(available online - http://www.univie.ac.at/hwastro/)
Stoeffler, Johannes , Stoeffler's Elucidatio - The Construction and Use of the Astrolabe,
English translation by Alessandro Gunella and John Lamprey, Classical Science
Press, 2007
Zachary, Michael, The Astrolabe Part 1: Understanding the Astrolabe, The Compleat
Anachronist number 147, 2010
Zachary, Michael, The Astrolabe Part 2: Constructing the Astrolabe, The Compleat
Anachronist number 148, 2010
Zotti, Georg. Tangible Heritage: Production of Astrolabes on a Laser Engraver
Astrolabe Resources
Websites: (I haven’t checked these lately)
http://astrolabes.org - James Morrison's Site
http://astrolabeproject.com –home of the Astrolabe Generator
http://www.astro.com/swisseph/swepha_e.htm - ephemeris source. PDF files
http://www.autodidacts.f2s.com/astro/index.html - Keith's Astrolabe
http://www.ted.com/talks/tom_wujec_demos_the_13th_century_astrolabe.html
http://www.mhs.ox.ac.uk/astrolabe/ - an online collection of astrolabes
http://www.puzzlering.net/astrolabe.html - Currently the only commercially
available astrolabe of any quality.
Software:
The Astrolabe Generator – free and open-source. Generates custom PostScript (EPS) files
allowing you to print out and build your own astrolabes http://astrolabeproject.com **This is where your astrolabe template came from.
There’s a wealth of information there, and instructions on how to draw the
parts by hand.
Stellarium – A free and open-source planetarium program. Good for working astrolabe
problems and checking results. http://www.stellarium.org/
Shadows Pro – Sundial software that incorporates an astrolabe simulator –
http://pagesperso-orange.fr/blateyron/sundials/shadowspro/gb/index.html
Illustrating Shadows – Spreadsheets for calculating sundials and astrolabe plates
http://www.illustratingshadows.com/