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Astrolabe Cart
Brief Summary
“Whenever you look at a map, gaze at the stars or take down a phone number, think of
Baghdad. Long ago, brilliant scholars in this booming city studied geography, astronomy and
mathematics—and made advances that can still be felt every day. Great minds from many
lands gathered at a Baghdad library called the House of Wisdom, one of many centers of
learning in an era known as the Islamic Golden Age.” (Traveling p188)
Topics you can cover:
1) Telling the time with an astrolabe
2) General overview of astrolabes (history, instrument to tell time and many other things)
3) A deeper understanding of astrolabes, including other calculations you can make with the
astrolabe
A note on terminology: A phrase you may hear connected to the astrolabe is Islamic Science.
We would like to make the case for using ‘Arabic Science’ as a broader, more inclusive term,
whenever we can with our visitors. The people doing this science at this time (750-1200’s
C.E.) were under the rule of the Abbāsids, whose official language was Arabic, and the
research was mostly carried out in the Iraq of today, especially the city of Baghdad. Though
this science was closely linked to the Islamic religion, Muslims were not the only scientists
who contributed to this important body of knowledge.
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Equipment Needed
What you need:
1. Astrolabe Cart
2. Pewter Astrolabe (located in drawer at the back of the cart)
3. Laminated Astrolabe Explanation Sheets (located in drawer at the back of the cart)
4. Optional: Additional astrolabe resources/laptop. There are a few books and pamphlets
that are located in that same drawer.
Pewter astrolabe. Stored in
drawer in back of
cart
Cart ready to be moved.
Note the astrolabe is lying
flat on the cart, and is not up
on the hook.
Cart set-up with astrolabe on
hook
Laminated astrolabe
explanation pages
Set Up
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Remove large astrolabe from hook and put it flat on the cart
Make sure the back drawer is locked and come open when moving the cart
Move cart to desired location
Hang large astrolabe on the hook
Take out any desired materials from the drawer at the back of the cart
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Parts of an Astrolabe
Front:
Star Pointers
Limb
Plate
Rule
Rete
Back:
Alidade
RETE -The rete (REE-tee) is a rotating dial that represents heavenly bodies.
PLATE – Stationary part of the astrolabe showing lines for the horizon, altitudes, and other
measurements. A plate is specific to particular latitude.
Ours is 37.75o N.
STAR POINTERS -Pointers on the rete represent well-known stars.
RULE -The rule shows the position of the Sun and the time of day.
LIMB—around edge; top ring is noon, 24 divisions represent 24 hours.
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ALIDADE (on back) -The alidade (AL-i-dayd) helps measure the height of a star (altitude) in
the sky.
Suggested Ways of Presenting the Demo
Using an Astrolabe to Calculate the Time Day:
Imagine you are standing under a night sky of stars. The first step is to pick a major star you
know, e.g. Aldebaran, the red star in Taurus (in Space, just pick a particular spot or easy
target near the ceiling to use as your star “Aldebaran”).
1. Site the Star - Hold up astrolabe at eye level and move
alidade on back to sight on the star “Aldebaran.”. Be sure to hold
the astrolabe by the ring so that it stays level.
2. On the back, read the altitude on the scale around outside
edge (same on both ends).
3. Find star pointer - On the front of the astrolabe, find the star
pointer labeled Aldeberan.
4. Rotate the rete - Using the measurement from step 2, rotate
the rete until the Aldeberan star pointer meets the correct
altitude arc on the east side of the astrolabe (left side is for
rising).
This task is made harder because of a number of factors: there
are a lot of markings on the rete and most are in Arabic, the
engraved plate on the back can only be seen in parts as the rete
rotates and the astrolabe itself is also quite worn from hard use.
The next step can be a bit confusing, because there is a step
skipped (translating today’s date into the zodiac calendar is
typically done on the back of the astrolabe – this information is
completely missing from the exhibit astrolabe) for simplicity.
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5. Align the rule - Align the rule to the mark for Sagittarius 6 engraved on the rete’s inner
circle. This mark corresponds to the date November 14, 1000.
6. Find your time -Read your time on the outer rim of the astrolabe, marked off by the rule.
Find Sunset and Sunrise
1. On the back, find a chosen date (today, your birthday, etc.), and use the alidade as a
guide to find the corresponding Zodiac date.
2. On rete, find the offset circle with zodiac names. Find zodiac date – this shows where
the Sun would be in relation to the other stars on that date. Place small circle sticker
on that position.
3. Move the sun to align with the horizon, both in rising and setting positions.
4. Move the rule to align with that Sun position.
5. Read the time off the limb: noon is at the top, count letters clockwise to the rule (each
letter=1 hour).
This is something that is also easily done with the laminated aides
Discuss some other uses of astrolabes:
One source states there are 1000 uses for the
astrolabe. These include surveying, planet
positions, longitude and latitude, horoscopes,
eclipses, rising times of stars, calculating sines
(mathematics), occultations, eclipses, and more.
(TED talk)
Islamic religious functions:
Finding the Quibla: Islamic astrolabes typically
have additional lines to find the quibla (the
direction to face while praying, i.e. the direction of
Mecca)
http://www.hps.cam.ac.uk/starry/isaslabereligion.h
tml
Prayer times: Islamic astrolabes have a special
set of markings to help calculate the five times of
day for prayer - daybreak, midday, mid-afternoon,
sunset, and dusk.
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When is Orion visible in the night sky?
Have visitors look for the two major stars in Orion, represented
by the small circles labeled B for Betelgeuse (left shoulder,
facing) and R for Rigel (right foot, facing). Then move the B/R
star pair high above the horizon. Since you can only see Orion
when it is nighttime, you need to find which months have the
Sun below the horizon at the same time that Orion is above the
horizon.
For example, if the B/R Orion star pair is as high in the sky as
possible, the suns below the horizon are October – March.
Meaning at night this constellation is visible in the winter
months in our northern hemisphere!
You can also use the small astrolabe.
Arabic Constellations
Four Arabic constellations can be seen on the back board of the cart. These constellation
images were inspired by drawings in the Book of Stars (see above).
The constellation Orion from Abd al-Rahman al-Sufi’s Book of Stars (image left). This
manuscript combined and expanded upon astronomical knowledge translated from Greek,
Persian and Arab texts. (Travelling p193)
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This illustration from an Arabic book of stars shows the constellation Orion. The bright star at
Orion’s left shoulder (facing - which means on the left when you LOOK at the constellation) is
Betelgeuse. The manuscript is believed to be a copy of the original and located at the Art
Archive/Bodleian Library Oxford, Marsh 144 Folio 325 (Travelling p193)
Stars in Orion (People and the Sky p33-34):
al Jabbār (“the giant”). The root of this word means “unifying
broken parts into an enlarged whole” and is the same as the root
of the word “algebra.”
The string of stars above Orion’s right shoulder (facing), is the
lion’s skin the hunter holds up = al Kumm (which means the
sleeve)
Note the similarities of three of the modern and Arabic names, in bold.
Arabic Name, meaning
Al Jabbar, the giant
Ibt al Jauzah, armpit of the
central one
Riji Jauzah al Yusra
Modern Name, description
Orion, hunter
Betelgeuse, bright red star
Rigel, bright blue star marks
right leg (facing)
Golden nuggets:
Orion’s Belt (3 bluish stars)
Mintaka = belt (on right)
Mintaka
Alnilam = string of pearls set Alnilam
in center of belt
Alnitak
Alnitak = girdle (last to rise)
al Murzim, roaring conqueror Bellatrix (right shoulder,
facing)
Saiph, sword
Saiph (left leg,facing)
al Kumm, the sleeve
(lion’s skin the hunter holds
up)
Operating Tips
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Always remove the large astrolabe from hook and place in drawer when you move the
cart so it does not swing and hit the star field.
Please keep an eye on the pewter astrolabe. If you chose not to use it, please keep it
in drawers so it does not walk away.
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Laminated Astrolabe Guides. These should be returned to the labeled folder when not
in use.
Take Down Procedure
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Secure small astrolabe, laminated pages, and other resources used in the drawer on
the back of the cart
Turn the silver knob on the back of the cart so that the drawer does not come out
during transport.
Take large astrolabe off of hook, and lay flat on exploration station while transporting
Understanding of the Astrolabe in Relation to the Sky
Visual Aides: a number of laminated images (including moveable parts) are on the cart to
assist in these explanations.
Color note: Though printed here in black and white, the colors are noted here and will be
evident on the E-station versions.
The astrolabe is a 2D object that maps the 3D movement
of the stars (including our sun). Let’s take a step back
and look at what is happening in the 3D world:
--The Earth is represented by brown ground at the
bottom.
--The sky’s ‘dome’ or what we can see above the
horizon, is represented by the half sphere.
--The cardinal directions are marked: east – south –
west – north.
--The sun is the dot (yellow) that follows a pathway
across the sky (curved yellow line rising in the east,
setting in the west). This pathway is slightly different each
day of the year – generally lower (closer to S) in the
winter and higher (closer to the zenith, green dot at top of sphere) in the summer.
To figure out the sun’s (or any star’s) location in this 3D world, you need to know two
things:
1. Altitude=height above horizon. The (purple) circle partly up the edge of the sphere shows
the sun’s altitude in this example. Note that the Sun’s path crosses this line twice – once in
the morning and once in the evening.
2. Azimuth=direction, or where on our 360o circle of earth it is found. This compass direction
is marked by an arrow (green). In this example it is about 135o from North, located between
South and East.
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How do the above 3D facts translate into the 2D
astrolabe?
--The Earth and what we can’t see below the horizon is
represented by the dark solid (brown) area.
--The sky’s ‘dome’ or what we can see above the
horizon is represented by the rest of the circle (teal) that
is not dark (brown).
--The cardinal directions are marked: east (left) – south
(top) – west (right) – north (bottom). The horizon line is
obvious (meeting of earth/brown and sky/teal). The
zenith is the off center dot (green).
--The sun is the dot (yellow) that follows a pathway
across the sky (circular yellow line, imagine the sun
rising in the east and setting in the west). This circular
pathway is slightly different each day of the year – generally smaller (setting earlier) in the
winter and larger (setting later) in the summer.
To figure out the sun’s (or any star’s) location for our 2D astrolabe, you need to know two
things:
1. Altitude=height above horizon. The off center (purple) circle that goes around the zenith
shows the sun’s altitude in this example. Note that the sun crosses this line twice – once in
the morning and once in the evening. Don’t forget, when using an astrolabe, NEVER look
directly at the sun. Align the sun’s shadow on the alidade to read the altitude, rather than
sighting through it as you would a more distant star.
2. What day it is. From the date, the astrolabe calculates the sun’s azimuth=direction, or
where on our 360 degree circle of earth it is found. This compass direction is marked by an
arrow (green). In this example it is about 135 degree from north, located between south and
east.
The e-station astrolabes have been calibrated to our 21st century.
House of Wisdom and Astrolabe History
House of Wisdom
 Starting in the late 700’s, the House of Wisdom in Baghdad established the
fundamentals of the process of science as we know it today. Science and religion
worked hand in hand to better understand and explain the world. What was
happening?
 The Koran told them to go out and study the world, and apply their new understanding
to deepen their understanding of the Koran. They didn’t distinguish at that time
between religious and scientific knowledge. (Pathfinders pxxviii)
 They deliberately sought knowledge wherever they could find it – Greek, Roman,
Indian knowledge was gathered and translated. This was the first time that these
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diverse studies were gathered together and studied as a whole. This metadata allowed
a new synthesis and set the stage for more learning. (Pathfinders p80)
These scientists found inconsistencies in this data and actively tried to figure out why –
they were firm believers in logic and close observation. This was the first time that the
‘rule of science’ was applied systematically. Muhammad ibn Zakariya changed the
practice of science with his ideas. He put out meat in different parts of the city to try to
figure out where the most sanitary place (=which animal rotted the least) to build a
hospital would be. Though they had no concept of microbes, they used observable
data to make decisions. (Traveling p189)
Astrolabe History
 Astrolabes are stunning things: at once artistic and scientific. Astrolabes may have
been invented as early as 400 B.C.E. The first known reference is found in writings by
Hipparchus, a Greek astronomer and mathematician, in 150 B.C.E. At first they were
simple devices used for astronomical problems, and over time they became more
complex, more elaborate, and more beautiful.
 Around 750 C.E., Al-Fazāri, astronomy advisor to the Bagdad Caliph, is credited with
building the first astrolabe in the Muslim world. Arabic astronomers added important
elements such as:
 Adding the azimuth marks along the horizon line (to help calculate direction of Mecca)
(Wiki-Astrolabe, Medieval Era). Note that the astrolabes in the interactive exhibit and
on the e-station do not have these markings.
 In the late 1000’s, they created the first ‘universal’ astrolabe, which was usable at
different latitudes. (Pathfinders p198)
Astrology in Baghdad
Astrology is the art of tracking the stars for horoscopes which was an important part of
Sasanian (Persian) daily life and part of the Zoroastrian mythology. The Islamic Abbāsid
caliph, al Mansūr (755-775 C.E.), employed astrologers to cast horoscopes and offer advice.
Not surprisingly, astronomy texts containing mathematical calculations and star chars from
Hindu and Greek astronomers were some of the first texts to be translated in the House of
Wisdom established by the Caliph in 762 C.E. in Baghdad. There was a lot of early interest in
astrology as they were working to reconcile two traditions: Islamic and Persian (Traveling
p181). However, over the next hundred years, astrology came into question as a science.
(Pathfinders p40-43)
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Background materials
collections links)
(websites,
videos,
articles,
digital
This manual draws heavily on a number of sources, noted below
Reference
Traveling the Silk Road: Ancient Pathways
to the Modern World by Mark Norell, Denise
Patry Leidy, and The American Museum of
Natural History (Sterling Signature, 2011)
Pathfinders: The Golden Age of Arabic
Astronomy, by Jim Al-Khalili
Ancient Astronomers by Anthony F. Aveni
People and the Sky by Anthony F. Aveni
TED talk: Tom Wujec: Learn to use the
13th-century astrolabe
Abbreviation in training manual
Traveling
Pathfinders
Ancient Astronomers
People and the Sky
TED talk
Also:
http://astrolabeproject.com/downloads/Astrolabe_in_Theory_and_Practice_Version_4.pdf
http://www.muslimheritage.com/article/using-astrolabe
http://www.astrolabes.org/
http://www.hps.cam.ac.uk/starry/isaslabe.html
Large astrolabe graphic and pewter astrolabes, by Norman Greene of Berkeley, CA.
http://www.puzzlering.net/astrolabe.html