Hello andychow
This is an astrolabe from the Islamic world, mediaeval or perhaps somewhat later.
The astrolabe was an astronomical/mathematical tool, known in Greece
in the second century BC, but later developed by Arab astronomers. In
the Middle Ages they were used throughout the Arab world, and spread
into Europe, for astronomical and astrological calculations, including
calculations for navigation, and calculations relating to the
calendar, religious festivals and times for prayer. The astrolabe was
widespread enough for one writer to say "its extensive development in
Islam made it the pocket watch of the medievals."
Astrolabes vary, but each one has a disc with degrees marked round the
edge. Within that is a plate engraved with markings for azimuth and
altitude at a particular latitude. Some astrolabes came with multiple
plates, but in the 10th century Ali ibn Khalf invented a single-plate
astrolabe, usable at a range of latitudes. Laid over this would be the
"rete", a disc with much of the metal cut away, showing the ecliptic
and some fixed stars. Then there might be a pointer, a "rule" or
"alidade". (Is this the straight metal bar which looks like part of
the rete in your picture? Or is the alidade missing?) The different
layers are held together with a pin and the astrolabe is suspended
from a ring, connected to the whole by a "kursi".
"The back of the instrument was engraved with a wide variety of scales
depending on where and when the astrolabe was made. All astrolabes
included scales for measuring angles and scales for determining the
Sun's longitude for any date. Additional scales were included at the
maker's option. Almost all European astrolabes, and many Islamic ones,
had a scale for solving simple trigonometry problems called the shadow
square. A cotangent scale was added to many Islamic astrolabes for
determining prayer times. Islamic instruments might also include a
scale for finding the direction to Mecca (the qibla), mathematical
scales of sines and cosines or astrological information. [...]
The back of every astrolabe included an alidade for measuring the
altitude of celestial objects. "
http://www.astrolabes.org/parts.htm
From here on I'll offer you excerpts from websites which I imagine
you'll want to explore further. Later I'll discuss the question of
date and add further references.
"There are several different types of astrolabes. By far the most
popular type is the planispheric astrolabe, on which the celestial
sphere is projected onto the plane of the equator. A planispheric
astrolabe consists of two flat circular disks. One of the disks has a
map of the sky on its face. The second disk shows the horizon, the
lines of altitude for a specific latitude and the zenith [...]The
astrolabe is mounted in a case with degrees marked around the
perimeter and arms mounted in the center. To use the astrolabe, you
move the moveable arms to a particular location.
'Astrolabes can be used to solve many astronomical problems that
would otherwise require rather sophisticated mathematics. All of the
everyday uses of the astrolabe are not known, but they were certainly
used to tell time during the day or night, to find the time of sunrise
and sunset and, thus, the length of the day, to locate celestial
objects in the sky, as a handy reference of celestial positions and,
as astrology was a deeply embedded element of the cultures that used
astrolabes, to determine aspects of horoscopes. Islamic prayer times
are astronomically determined, and the astrolabe could be used to
determine the required times' (Morrison, 2000).
Another kind of astrolabe was a navigational astrolabe. The astrolabe
allowed a sailor to determine his latitude--the north-south position.
To do this, the sailor would align the horizontal axis of the
astrolabe with the horizon. He then pointed it at the sun and read its
position on the outer disk. He could then find his latitude by
consulting an astronomical table (usually in a book)."
http://www.mastep.sjsu.edu/history_of_tech/islam.htm
* * * *
"Eighth century literary references from Baghdad and Damascus indicate
that by this time the use of the astrolabe was widespread throughout
the Arab world. Land under Arab control stretched from North Africa
and Spain to India, enabling a wide range of astronomical influences
to be combined. The early ninth-century tables of al-Farghânî list the
radii of the circles on the plate of the astrolabe for each degree of
latitude. These simplified the process of astrolabe construction by
removing the need for mathematical calculation of these values,
indicating that astrolabes were being manufactured in substantial
numbers since the effort involved in producing the tables would have
been considerable. The earliest surviving Islamic astrolabes date from
the ninth century, and these are of such quality and craftsmanship
that they represent a continuing tradition rather than a new activity.
By the eleventh and twelfth centuries there are many surviving texts
and astrolabes, the instruments varying in style and artistry but
retaining many fundamental similarities in functionality and design.
http://www.hps.cam.ac.uk/starry/isaslabe.html
(I had some trouble with this link. You may have to go to the
Cambridge History and Philosophy of Science search page and enter
"Islamic astrolabe":
http://www.hps.cam.ac.uk/search.html )
* * * *
"The astrolabe, whose mathematical theory is based on the
stereographic projection of the sphere, was invented in late
antiquity, but its extensive development in Islam made it the pocket
watch of the medievals. In its original form, it required a different
plate of horizon coordinates for each latitude, but in the 11th
century the Spanish Muslim astronomer az-Zarqallu invented a single
plate that worked for all latitudes. Slightly earlier, astronomers in
the East had experimented with plane projections of the sphere, and
al-Biruni invented such a projection that could be used to produce a
map of a hemisphere. The culminating masterpiece was the astrolabe of
the Syrian Ibn ash-Shatir (1305-75), a mathematical tool that could be
used to solve all the standard problems of spherical astronomy in five
different ways."
http://www-gap.dcs.st-and.ac.uk/~history/HistTopics/Arabic_mathematics.html
* * * *
" Ali ibn Khalaf in the tenth century invented the 'universal plate'
that provided a stereographic projection of the sphere on a plane
perpendicular to the ecliptic and cutting it according to the
solstitial line of Cancer-Capricorn. Al-Zarqali followed with his
famous instrument al-sailhah, an astrolabe in which the two
stereographic projections of the circles of the equator and the
ecliptic were presented on the same surface. His compatriot Jabir ibn
Aflah had also invented a 'universal instrument' to be used for
astronomy as well as mathematics and physics, an instrument which many
consider as the forerunner of the European torquetum. Following them
Muzaffar Sharaf al-Din al-Tusi in vented the linear astrolabe to
simplify the instrument."
://www.google.co.uk/search?q=cache:7GkahS285kcJ:www.kol.org/astrolabe.htm+Ali+ibn+Khalaf+astrolabe+plate&hl=en&ie=UTF-8
* * * *
"Both the plate and the rete were planar representations of the
spherical coordinate system of the sky. This type of representation is
called stereographic projection.
Stereographic projection is a mathematical means of transcribing any
three dimensional coordinate system on to a two dimensional plane."
http://members.aol.com/chopstcks/gca7sky/astrolabe.htm
* * * *
"Some astrolabes are genuine works of art rather than simply
astronomical calculating devices - elaborately engraved and
beautifully made. The decorator of the astrolabe was sometimes a
different person to the astrolabist who calculated the scales,
indicating that the astrolabe's function as a beautiful object was of
importance at the time it was made. Astrolabes seem to have been
highly prized possessions, and were treated as objects with a dual
purpose: functionality and beauty."
http://www.hps.cam.ac.uk/starry/isaslabepoems.html
* * * *
Dating your astrolabe accurately would need a specialist opinion,
unless there is a year inscribed on it, which you could discover by
asking someone who reads Arabic. You might enlarge the photograph and
increase the contrast using a graphics program, to see the script more
clearly. (I did this, which is why I'm so sure it's an Islamic
astrolabe.)
Searching for information on style, ornamentation and so on didn't
produce anything definitive, only this kind of general comment:
"There are a number of interesting stylistic differences between
astrolabes from the eastern Islamic areas (the Mashriq), Northern
Africa (the Maghrib) and Moorish Spain (Andalusia)."
http://www.astrolabes.org/history.htm
It's unlikely to be earlier than the thirteenth century since few of
the earliest astrolabes survive.
You could try asking for an opinion from one of the following museums,
which both include Islamic astrolabes in their collections:
Adler Planetarium & Astronomy Museum (Chicago)
http://www.adlerplanetarium.org/contactus/index.shtml
Science Museum (London)
http://www.sciencemuseum.org.uk/lets_talk/comments.asp
==================================================
The Cambridge University site I referred to earlier is extremely
useful and has splendid large, good quality photographs of some
astrolabes which I think will help enormously with clarifying the
astrolabe's use. I won't give you all the URLs here because the search
I explained above should lead you through the site, but be sure you
don't miss the picture of the back of an astrolabe showing the
alidade. The alidade seems to be absent in your example, which may
suggest it was not used for serious navigation.
http://www.hps.cam.ac.uk/starry/isaslabe1med.jpg
(Or is the straight bar of metal which appears to be part of the rete
in your picture usable as a pointer?)
Pictures of Astrolabes
======================
A Yemeni astrolabe from 1291:
"The object is composed of eight elements: case, alidade (rule), rete
(network), four uniform plates, and a bolt or pin that keeps the parts
in place. An astronomer would suspend the astrolabe by his thumb and
hold it toward the starry sky when he needed to consult it."
http://www.metmuseum.org/toah/ht/07/wap/ht07wap.htm
Said to be "the earliest known astrolabe" from 927
http://www.soas.ac.uk/gallery/Previous/IslamicPatronage/19.html
Persian astrolabe 1388
http://www.moa.ubc.ca/spiritofislam/unity/astrolabe.html
14c astrolabe
www.astroconsulting.com/FAQs/arabic.htm
"Copy of an Islamic astronomical astrolabe showing the various
interchangeable plates for use with differing areas of the celestial
sphere."
http://www.westsea.com/tsg3/octlocker/octcapchart02.html
Mediaeval Arab astronomers using an astrolabe:
http://www.levity.com/alchemy/islam12.htm
Picture of a modern astronomer using an astrolabe
http://www.anl.gov/OPA/logos18-1/astrosidebar.htm
There are more pictures here:
http://images.google.co.uk/images?hl=en&lr=&ie=UTF-8&oe=UTF-8&q=astrolabe+islam+OR+islamic+OR+arabic+OR+arab&btnG=Google+Search
=========================================================
Further Reading
===============
As well as the websites I've already referred to, you might be
interested in some of these:
The Islamic Astrolabe
http://www.cod.edu/middle/history/astrolabe.pdf
Astrolabes in the Online Register of Scientific Instruments
http://www.isin.org/browse.asp?subject=heading&letter=As
From "Essays in Medieval Studies":
"The best survey of instruments is Gunther's The Astrolabes of the World, 2 vols.
(Oxford: Oxford University Press, 1932).
On the Arabic terms for the astrolabe, see Dwight M. Donaldson,
"The Nomenclature and Common Uses of the Astrolabe," Islamic Culture,
19 (1945), 49-53. The best account of the instrument's workings is
Henri Michel,
Traité de l'astrolabe (Paris: Gauthier- Villars, 1947). Also helpful
are Francis Maddison, "Early Astronomical and Mathematical
Instruments: A Brief Survey of Sources and Modern Studies," History of
Science, 2 (1963), 17-50,
and the three studies of Emmanuel Poulle,
"L'astrolabe médiéval d'après les manuscripts de la Bibliothèque
Nationale," Bibliothèque de l'École de Cartes, 112 (1954), 81-103,
"Peut-on dater les astrolabes médiévaux?" Revue d'Histoire des
Sciences, 9 (1956), 301-322,
and "Le traité d'astrolabe de Raymond de Marseille," Studi medievali,
3a Ser., 5 (1964), 866-900. "
http://www.luc.edu/publications/medieval/vol1/1ch6n.html
The History and Practice of Ancient Astronomy by James Evans
http://www.amazon.com/exec/obidos/tg/detail/-/0195095391/qid=1068217791/sr=1-3/ref=sr_1_3/103-3406958-0055841?v=glance&s=books
And these recommendations come from the Cambridge History of Science site:
Sarah Schechener Genuth: "Astrolabes: a Cross-Cultural and Social Perspective"
introduction to Webster (ed) Western Astrolabes
David King: Astronomy in the Service of Islam 1993
John North: The Fontana History of Astronomy and Cosmology, London 1994
David King: Astronomy for Landlubbers and Navigators: the case of the
Islamic Middle Ages, 1984
David King: Islamic Astronomical Instruments 1987
Anthony Turner: Astrolabes, Astrolabe related instruments 1985 (introduction)
Please don't heistate to ask if you would like me to try to find any
of these books in a library near you, or find a copy for sale. You
are, of course, welcome to ask if you have any queries and I'll do my
best to help. Also, do let me know if any links fail to work.
I hope you find this material on astrolabes as interesting as I have,
and can make use of it in your research.
Best wishes - Leli
Search strategy:
I thought this might be an astrolabe, so started with a google images
search to confirm:
http://images.google.co.uk/images?q=astrolabe&ie=UTF-8&oe=UTF-8&hl=en&btnG=Google+Search
Then I enlarged your picture and increased the contrast levels, as I
already described, and saw the Arabic, or Persian, script. I did
consider the possibility that it was Urdu or another Indian script
related to Arabic writing, but even though I admit the picture quality
is not good enough for certainty, I feel confident it is not Urdu.
Subsequent searches used combinations of
astrolabe astrolabes
islamic islam arabic arab
decorative
silver
brass
style
art
stylistic
mediaeval
medieval
alidade
rete
astrology
astronomy |
