An astrolabe (
Greek: ἀστρολάβοςastrolábos, 'star-taker';
Arabic: ٱلأَسْطُرلابal-Asṭurlāb;
Persian: ستارهیابSetāreyāb) is an
astronomical instrument dating to ancient times. It serves as a
star chart and
physical model of visible
heavenly bodies. Its various functions also make it an elaborate
inclinometer and an
analog calculation device capable of working out several kinds of problems in astronomy. In its simplest form it is a metal disc with a pattern of wires, cutouts, and perforations that allows a user to calculate astronomical positions precisely. It is able to measure the
altitude above the horizon of a celestial body, day or night; it can be used to identify stars or planets, to determine local
latitude given
local time (and vice versa), to survey, or to
triangulate. It was used in
classical antiquity, the
Islamic Golden Age, the European
Middle Ages and the
Age of Discovery for all these purposes.
The astrolabe, which is a precursor to the
sextant,[1] is effective for determining latitude on land or calm seas. Although it is less reliable on the heaving deck of a ship in rough seas, the
mariner's astrolabe was developed to solve that problem.
Applications
A 10th-century astronomer
Abd Al-Rahman Al-Sufi wrote a massive text of 386 chapters on the astrolabe. His work described more than 1000 applications for the astrolabe's various functions.[2] These ranged from the astrological, the astronomical and the religious, to navigation, seasonal and daily time-keeping, and tide tables. At the time of their use, astrology was widely considered as much of a serious science as astronomy, and study of the two went hand-in-hand. The astronomical interest varied between folk astronomy (of the pre-Islamic tradition in Arabia) which was concerned with celestial and seasonal observations, and mathematical astronomy, which would inform intellectual practices and precise calculations based on astronomical observations. In regard to the astrolabe's religious function, the demands of Islamic prayer times were to be astronomically determined to ensure precise daily timings, and the
qibla, the direction of
Mecca towards which Muslims must pray, could also be determined by this device. In addition to this, the
lunar calendar that was informed by the calculations of the astrolabe was of great significance to the religion of Islam, given that it determines the dates of important religious observances such as
Ramadan.[citation needed]
Etymology
The Oxford English Dictionary gives the translation "star-taker" for the English word astrolabe and traces it through medieval Latin to the
Greek word ἀστρολάβος : astrolábos,[3][4] from ἄστρον : astron "star" and λαμβάνειν : lambanein "to take".[5]
In the medieval Islamic world the
Arabic word al-Asturlāb (i.e., astrolabe) was given various etymologies. In Arabic texts, the word is translated as ākhidhu al-Nujūm (
Arabic: آخِذُ ٱلنُّجُومْ,
lit.'star-taker'), a direct translation of the Greek word.[6]
Al-Biruni quotes and criticises medieval scientist
Hamza al-Isfahani who stated:[6] "asturlab is an arabisation of this Persian phrase" (sitara yab, meaning "taker of the stars").[7] In
medieval Islamic sources, there is also a
folk etymology of the word as "lines of lab", where "Lab" refers to a certain son of
Idris (
Enoch). This etymology is mentioned by a 10th-century scientist named
al-Qummi but rejected by
al-Khwarizmi.[8]
History
Ancient world
An early astrolabe was invented in the
Hellenistic civilization by
Apollonius of Perga between 220 and 150 BC, often attributed to
Hipparchus. The astrolabe was a marriage of the
planisphere and
dioptra, effectively an analog calculator capable of working out several different kinds of problems in astronomy. Another related device, used for similar purposes in the ancient world, is the
armillary sphere.
Theon of Alexandria (
c. 335 –
c. 405) wrote a detailed treatise on the astrolabe, and Lewis[9] argues that
Ptolemy used an astrolabe to make the astronomical observations recorded in the Tetrabiblos. The invention of the plane astrolabe is sometimes wrongly attributed to Theon's daughter
Hypatia (
c. 350–370; died AD 415),[10][11][12][13] but it's known to have been used at least 500 years earlier.[11][12][13] The misattribution comes from a misinterpretation of a statement in a letter written by Hypatia's pupil
Synesius (
c. 373 –
c. 414),[11][12][13] which mentions that Hypatia had taught him how to construct a plane astrolabe, but does not say that she invented it.[11][12][13]
Astrolabes continued in use in the Greek-speaking world throughout the
Byzantine period. About AD 550, Christian philosopher
John Philoponus wrote a treatise on the astrolabe in Greek, which is the earliest extant treatise on the instrument.[a] Mesopotamian bishop
Severus Sebokht also wrote a treatise on the astrolabe in the
Syriac language in the mid-7th century.[b] Sebokht refers to the astrolabe as being made of brass in the introduction of his treatise, indicating that metal astrolabes were known in the Christian East well before they were developed in the Islamic world or in the Latin West.[14]
The first Renaissance treatises dealing with scientific problems were based on earlier classical works and were often concerned with Ptolemaic doctrines.[citation needed]
The mathematical background was established by Muslim astronomer
Albatenius in his treatise Kitab az-Zij (c. AD 920), which was translated into Latin by
Plato Tiburtinus (De Motu Stellarum). The earliest surviving astrolabe is dated
AH 315 (AD 927–928). In the Islamic world, astrolabes were used to find the times of sunrise and the rising of fixed stars, to help schedule morning prayers (
salat). In the 10th century,
al-Sufi first described over 1,000 different uses of an astrolabe, in areas as diverse as
astronomy,
astrology,
navigation,
surveying, timekeeping, prayer,
Salat,
Qibla, etc.[18][19]
The
spherical astrolabe was a variation of both the astrolabe and the
armillary sphere, invented during the
Middle Ages by astronomers and
inventors in the Islamic world.[c] The earliest description of the spherical astrolabe dates to
Al-Nayrizi (
fl. 892–902). In the 12th century,
Sharaf al-Dīn al-Tūsī invented the linear astrolabe, sometimes called the "staff of al-Tusi", which was "a simple wooden rod with graduated markings but without sights. It was furnished with a plumb line and a double chord for making angular measurements and bore a perforated pointer".[20] The geared mechanical astrolabe was invented by Abi Bakr of
Isfahan in 1235.[21]
The first known metal astrolabe in Western Europe is the Destombes astrolabe made from brass in the eleventh century in Portugal.[22][23] Metal astrolabes avoided the warping that large wooden ones were prone to, allowing the construction of larger and therefore more accurate instruments. Metal astrolabes were heavier than wooden instruments of the same size, making it difficult to use them in navigation.[24]
Herman Contractus of
Reichenau Abbey, examined the use of the astrolabe in Mensura Astrolai during the 11th century.[25]Peter of Maricourt wrote a treatise on the construction and use of a universal astrolabe in the last half of the 13th century entitled Nova compositio astrolabii particularis. Universal astrolabes can be found at the History of Science Museum in Oxford.[26] David A. King, historian of Islamic instrumentation, describes the universal astrolobe designed by Ibn al-Sarraj of
Aleppo (aka Ahmad bin Abi Bakr; fl. 1328) as "the most sophisticated astronomical instrument from the entire Medieval and Renaissance periods".[27]
English author
Geoffrey Chaucer (c. 1343–1400) compiled A Treatise on the Astrolabe for his son, mainly based on a work by
Messahalla or
Ibn al-Saffar.[28][29] The same source was translated by French astronomer and astrologer Pélerin de Prusse and others. The first printed book on the astrolabe was Composition and Use of Astrolabe by
Christian of Prachatice, also using Messahalla, but relatively original.
In 1370, the first Indian treatise on the astrolabe was written by the
Jain astronomer
Mahendra Suri, titled Yantrarāja.[30]
A simplified astrolabe, known as a balesilha, was used by sailors to get an accurate reading of latitude while at sea. The use of the balesilha was promoted by
Prince Henry (1394–1460) while navigating for Portugal.[31]
The astrolabe was almost certainly first brought north of the Pyrenees by Gerbert of Aurillac (future
Pope Sylvester II), where it was integrated into the
quadrivium at the school in Reims, France, sometime before the turn of the 11th century.[32] In the 15th century, French instrument maker Jean Fusoris (c. 1365–1436) also started remaking and selling astrolabes in his shop in
Paris, along with portable sundials and other popular scientific devices of the day.
Thirteen of his astrolabes survive to this day.[33] One more special example of craftsmanship in early 15th-century Europe is the astrolabe designed by Antonius de Pacento and made by Dominicus de Lanzano, dated 1420.[34]
In the 16th century,
Johannes Stöffler published Elucidatio fabricae ususque astrolabii, a manual of the construction and use of the astrolabe. Four identical 16th-century astrolabes made by
Georg Hartmann provide some of the earliest evidence for
batch production by
division of labor. In 1612, Greek painter
Ieremias Palladas incorporated a sophisticated astrolabe in his painting depicting Catherine of Alexandria. The painting was entitled Catherine of Alexandria and featured a device called the System of the Universe (Σύστημα τοῦ Παντός). The device featured the planets with the names in Greek:
Selene (Moon),
Hermes (Mercury),
Aphrodite (Venus),
Helios (Sun),
Ares (Mars),
Zeus (Jupiter), and
Chronos (Saturn). The device also featured celestial spheres following the Ptolemaic model and Earth was depicted as a blue sphere with circles of geographic coordinates. A complex line representing the axis of the Earth covered the entire instrument.[35]
Medieval astrolabes
A treatise explaining the importance of the astrolabe by
Nasir al-Din al-Tusi, Persian scientist
A page from the 1575 book "Astrolabium" depicting an astrolabe. Masha'Allah
Public Library Bruges [
nl] Ms. 522
Astrolabes and clocks
Mechanical
astronomical clocks were initially influenced by the astrolabe; they could be seen in many ways as clockwork astrolabes designed to produce a continual display of the current position of the sun, stars, and planets. For example,
Richard of Wallingford's clock (c. 1330) consisted essentially of a star map rotating behind a fixed rete, similar to that of an astrolabe.[36]
Many astronomical clocks use an astrolabe-style display, such as the famous
clock at Prague, adopting a stereographic projection (see below) of the ecliptic plane. In recent times, astrolabe watches have become popular. For example, Swiss watchmaker
Ludwig Oechslin designed and built an astrolabe wristwatch in conjunction with
Ulysse Nardin in 1985.[37] Dutch watchmaker Christaan van der Klauuw also manufactures astrolabe watches today.[38]
Above the mater and tympan, the rete, a framework bearing a projection of the
ecliptic plane and several
pointers indicating the positions of the brightest
stars, is free to rotate. These pointers are often just simple points, but depending on the skill of the craftsman can be very elaborate and artistic. There are examples of astrolabes with artistic pointers in the shape of balls, stars, snakes, hands, dogs' heads, and leaves, among others.[39] The names of the indicated stars were often engraved on the pointers in Arabic or Latin.[40] Some astrolabes have a narrow rule or label which rotates over the rete, and may be marked with a scale of
declinations.
The rete, representing the
sky, functions as a
star chart. When it is rotated, the stars and the
ecliptic move over the projection of the coordinates on the tympan. One complete rotation corresponds to the passage of a day. The astrolabe is, therefore, a predecessor of the modern
planisphere.
On the back of the mater, there is often engraved a number of scales that are useful in the astrolabe's various applications. These vary from designer to designer, but might include curves for time conversions, a
calendar for converting the day of the month to the sun's position on the ecliptic, trigonometric scales, and graduation of 360 degrees around the back edge. The alidade is attached to the back face. An alidade can be seen in the lower right illustration of the Persian astrolabe above. When the astrolabe is held vertically, the alidade can be rotated and the sun or a star sighted along its length, so that its altitude in degrees can be read ("taken") from the graduated edge of the astrolabe; hence the word's Greek roots: "astron" (ἄστρον) = star + "lab-" (λαβ-) = to take. The alidade had vertical and horizontal cross-hairs which plots locations on an azimuthal ring called an almucantar (altitude-distance circle).
An arm called a radius connects from the center of the astrolabe to the optical axis which is parallel with another arm also called a radius. The other radius contains graduations of altitude and distance measurements.
A shadow square also appears on the back of some astrolabes, developed by Muslim astrologists in the 9th Century, whereas devices of the Ancient Greek tradition featured only altitude scales on the back of the devices.[41] This was used to convert shadow lengths and the altitude of the sun, the uses of which were various from surveying to measuring inaccessible heights.[42]
Devices were usually signed by their maker with an inscription appearing on the back of the astrolabe, and if there was a patron of the object, their name would appear inscribed on the front, or in some cases, the name of the reigning sultan or the teacher of the astrolabist has also been found to appear inscribed in this place.[43] The date of the astrolabe's construction was often also signed, which has allowed historians to determine that these devices are the second oldest scientific instrument in the world. The inscriptions on astrolabes also allowed historians to conclude that astronomers tended to make their own astrolabes, but that many were also made to order and kept in stock to sell, suggesting there was some contemporary market for the devices.[43]
Construction of astrolabes
The
Hartmann astrolabe in
Yale collection. This instrument shows its rete and rule.
Celestial Globe, Isfahan (?), Iran 1144. Shown at the
Louvre Museum, this globe is the third oldest surviving in the world.
Computer-generated planispheric astrolabe
Mathematical basis
The construction and design of astrolabes are based on the application of the
stereographic projection of the
celestial sphere. The point from which the projection is usually made is the
South Pole. The plane onto which the projection is made is that of the
Equator.[44]
Designing a tympanum through stereographic projection
The tympanum captures the celestial coordinate axes upon which the rete will rotate. It is the component that will enable the precise determination of a star's position at a specific time of
day and
year.
Therefore, it should project:
The
zenith, which will vary depending on the
latitude of the astrolabe user.
The
horizon line and
almucantar or circles parallel to the horizon, which will allow for the determination of a celestial body's
altitude (from the horizon to the zenith).
The
celestial meridian (north-south meridian, passing through the zenith) and secondary meridians (circles intersecting the north-south meridian at the zenith), which will enable the measurement of
azimuth for a celestial body.
When projecting onto the celestial equatorial plane, three concentric circles correspond to the celestial sphere's three
circles of latitude (left side of the image). The largest of these, the projection on the celestial equatorial plane of the celestial
Tropic of Capricorn, defines the size of the astrolabe's tympanum. The center of the tympanum (and the center of the three circles) is actually the north-south axis around which Earth rotates, and therefore, the rete of the astrolabe will rotate around this point as the hours of the day pass (due to
Earth's rotational motion).
The three concentric circles on the tympanum are useful for determining the exact moments of
solstices and
equinoxes throughout the year: if the sun's altitude at noon on the rete is known and coincides with the outer circle of the tympanum (Tropic of Capricorn), it signifies the
winter solstice (the sun will be at the
zenith for an observer at the Tropic of Capricorn, meaning summer in the southern hemisphere and winter in the northern hemisphere). If, on the other hand, its altitude coincides with the inner circle (Tropic of Cancer), it indicates the
summer solstice. If its altitude is on the middle circle (equator), it corresponds to one of the two
equinoxes.
The horizon and the measurement of altitude
On the right side of the image above:
The blue arrow indicates the direction of true north (the
North Star).
The central blue point represents Earth (the observer's location).
The black arrow represents the
zenith direction for the observer (which would vary depending on the observer's
latitude).
The two black circles represent the
horizon surrounding the observer, which is perpendicular to the zenith vector and defines the portion of the
celestial sphere visible to the observer, and its projection on the celestial equatorial plane.
The geographic south of the celestial sphere acts as the
projection pole.
When projecting the
horizon onto the celestial equatorial plane, it transforms into an ellipse upward-shifted relatively to the center of the tympanum (both the observer and the projection of the north-south axis). This implies that a portion of the celestial sphere will fall outside the outer circle of the tympanum (the projection of the celestial
Tropic of Capricorn) and, therefore, won't be represented.
Additionally, when drawing circles parallel to the horizon up to the zenith (
almucantar), and projecting them on the celestial equatorial plane, as in the image above, a grid of consecutive ellipses is constructed, allowing for the determination of a
star's altitude when its rete overlaps with the designed tympanum.
The meridians and the measurement of azimuth
On the right side of the image above:
The blue arrow indicates the direction of true north (the
North Star).
The central blue point represents Earth (the observer's location).
The black arrow represents the
zenith direction for the observer (which would vary depending on the observer's
latitude).
The two black circles represent the
horizon surrounding the observer, which is perpendicular to the zenith vector and defines the portion of the
celestial sphere visible to the observer, and its projection on the celestial equatorial plane.
The five red dots represent the
zenith, the
nadir (the point on the
celestial sphere opposite the zenith with respect to the observer), their projections on the celestial equatorial plane, and the center (with no physical meaning attached) of the circle obtained by projecting the secondary meridian (see below) on the celestial equatorial plane.
The orange circle represents the
celestial meridian (or meridian that goes, for the observer, from the north of the horizon to the south of the horizon passing through the zenith).
The two red circles represent a secondary meridian with an
azimuth of 40° East relative to the observer's horizon (which, like all secondary meridians, intersects the principal meridian at the zenith and nadir), and its projection on the celestial equatorial plane.
The geographic south of the celestial sphere acts as the
projection pole.
When projecting the
celestial meridian, it results in a straight line that overlaps with the vertical axis of the tympanum, where the
zenith and
nadir are located. However, when projecting the 40° E meridian, another circle is obtained that passes through both the zenith and nadir projections, so its center is located on the perpendicular
bisection of the segment connecting both points. In deed, the projection of the celestial meridian can be considered as a circle with an infinite radius (a straight line) whose center is on this bisection and at an infinite distance from these two points.
If successive meridians that divide the celestial sphere into equal sectors (like "orange slices" radiating from the zenith) are projected, a family of curves passing through the zenith projection on the tympanum is obtained. These curves, once overlaid with the rete containing the major stars, allow for determining the
azimuth of a star located on the rete and rotated for a specific time of day.
^Modern editions of
John Philoponus' treatise on the astrolabe are De usu astrolabii eiusque constructione libellus (On the Use and Construction of the Astrolabe), ed. Heinrich Hase, Bonn: E. Weber, 1839,
OCLC165707441 (or id. Rheinisches Museum für Philologie 6 (1839): 127–71); repr. and translated into French by Alain Philippe Segonds, Jean Philopon, traité de l'astrolabe, Paris: Librairie Alain Brieux, 1981,
OCLC10467740; and translated into English by H.W. Green in R.T. Gunther, The Astrolabes of the World, Vol. 1/2, Oxford, 1932,
OL18840299M repr. London: Holland Press, 1976,
OL14132393M pp. 61–81.
^O'Leary, De Lacy (1948).
How Greek Science Passed to the Arabs. Routledge and Kegan Paul. "The most distinguished Syriac scholar of this later period was
Severus Sebokht (d. 666–7), Bishop of Kennesrin. [...] In addition to these works [...] he also wrote on astronomical subjects (Brit. Mus. Add. 14538), and composed a treatise on the astronomical instrument known as the astrolabe, which has been edited and published by F. Nau (Paris, 1899)." Severus' treatise was translated by Jessie Payne Smith Margoliouth in R.T. Gunther, Astrolabes of the World, Oxford, 1932, pp. 82–103.
^Savage-Smith, Emilie (1993). "Book Reviews". Journal of Islamic Studies. 4 (2): 296–299.
doi:
10.1093/jis/4.2.296. There is no evidence for the Hellenistic origin of the spherical astrolabe, but rather evidence so far available suggests that it may have been an early but distinctly Islamic development with no Greek antecedents.
^Nizamoglu, Cem (2005-08-10).
"Using an Astrolabe". Muslim Heritage. Retrieved 2023-10-16.
^Lachièz-Rey, Marc; Luminet, Jean-Pierre (2001). Celestial Treasury: From the Music of Spheres to the Conquest of Space. Translated by Joe Laredo. Cambridge, United Kingdom: Cambridge University Press. p. 74.
ISBN978-0-521-80040-2.
^"Introduction". The Astrolabe: an Online Resource. 2006. Retrieved 2020-05-15.
^Harley, J. B.; Woodward, David (1992). The history of cartography. Chicago, Illinois: University of Chicago Press. p. 31.
ISBN0-226-31635-1.
^Kunitzsch, Paul (1981). "On the authenticity of the treatise on the composition and use of the astrolabe ascribed to Messahalla". Archives Internationales d'Histoire des Sciences Oxford. 31 (106): 42–62.
^Ralf Kern (2010), Wissenschaftliche Instrumente in ihrer Zeit. Band 1: Vom Astrolab zum mathematischen Besteck. Cologne, S. 204.
ISBN978-3-86560-865-9
^
abStephenson, Bruce; Bolt, Marvin; Friedman, Anna Felicity (2000). The Universe Unveiled: Instruments and Images through History. Cambridge, UK: Cambridge University Press. pp. 108–109.
ISBN0-521-79143-X.
^King, David A. Some Medieval Astronomical Instruments and Their Secrets, in Mazzolini, R. G. (ed.), Non-Verbal Communication in Science prior to 1900.
Florence. p. 30.
^King, David A. (2018). The Astrolabe: What it is & what it is not. Frankfurt, Germany:
Frankfurt.
Evans, James (1998), The History and Practice of Ancient Astronomy, Oxford University Press,
ISBN0-19-509539-1.
Gunella, Alessandro; Lamprey, John (2007), Stoeffler's Elucidatio (translation of Elucidatio fabricae ususque astrolabii into English), John Lamprey
King, D. A. (1981), "The Origin of the Astrolabe According to the Medieval Islamic Sources", Journal for the History of Arabic Science, 5: 43–83
King, Henry (1978), Geared to the Stars: the Evolution of Planetariums, Orreries, and Astronomical Clocks, University of Toronto Press
Krebs, Robert E.; Krebs, Carolyn A. (2003), Groundbreaking Scientific Experiments, Inventions, and Discoveries of the Ancient World, Greenwood Press.
Laird, Edgar (1997), Carol Poster and Richard Utz (ed.), "Astrolabes and the Construction of Time in the Late Middle Ages.", Constructions of Time in the Late Middle Ages, Evanston, Illinois: Northwestern University Press: 51–69
Laird, Edgar; Fischer, Robert, eds. (1995), "Critical edition of Pélerin de Prusse on the Astrolabe (translation of Practique de Astralabe)", Medieval & Renaissance Texts & Studies, Binghamton, New York,
ISBN0-86698-132-2
Lewis, M. J. T. (2001), Surveying Instruments of Greece and Rome, Cambridge University Press.
Neugebauer, Otto E. (1975), A History of Ancient Mathematical Astronomy, Springer
North, John David (2005), God's Clockmaker: Richard of Wallingford and the Invention of Time, Continuum International Publishing Group,
ISBN978-1-85285-451-5
An astrolabe (
Greek: ἀστρολάβοςastrolábos, 'star-taker';
Arabic: ٱلأَسْطُرلابal-Asṭurlāb;
Persian: ستارهیابSetāreyāb) is an
astronomical instrument dating to ancient times. It serves as a
star chart and
physical model of visible
heavenly bodies. Its various functions also make it an elaborate
inclinometer and an
analog calculation device capable of working out several kinds of problems in astronomy. In its simplest form it is a metal disc with a pattern of wires, cutouts, and perforations that allows a user to calculate astronomical positions precisely. It is able to measure the
altitude above the horizon of a celestial body, day or night; it can be used to identify stars or planets, to determine local
latitude given
local time (and vice versa), to survey, or to
triangulate. It was used in
classical antiquity, the
Islamic Golden Age, the European
Middle Ages and the
Age of Discovery for all these purposes.
The astrolabe, which is a precursor to the
sextant,[1] is effective for determining latitude on land or calm seas. Although it is less reliable on the heaving deck of a ship in rough seas, the
mariner's astrolabe was developed to solve that problem.
Applications
A 10th-century astronomer
Abd Al-Rahman Al-Sufi wrote a massive text of 386 chapters on the astrolabe. His work described more than 1000 applications for the astrolabe's various functions.[2] These ranged from the astrological, the astronomical and the religious, to navigation, seasonal and daily time-keeping, and tide tables. At the time of their use, astrology was widely considered as much of a serious science as astronomy, and study of the two went hand-in-hand. The astronomical interest varied between folk astronomy (of the pre-Islamic tradition in Arabia) which was concerned with celestial and seasonal observations, and mathematical astronomy, which would inform intellectual practices and precise calculations based on astronomical observations. In regard to the astrolabe's religious function, the demands of Islamic prayer times were to be astronomically determined to ensure precise daily timings, and the
qibla, the direction of
Mecca towards which Muslims must pray, could also be determined by this device. In addition to this, the
lunar calendar that was informed by the calculations of the astrolabe was of great significance to the religion of Islam, given that it determines the dates of important religious observances such as
Ramadan.[citation needed]
Etymology
The Oxford English Dictionary gives the translation "star-taker" for the English word astrolabe and traces it through medieval Latin to the
Greek word ἀστρολάβος : astrolábos,[3][4] from ἄστρον : astron "star" and λαμβάνειν : lambanein "to take".[5]
In the medieval Islamic world the
Arabic word al-Asturlāb (i.e., astrolabe) was given various etymologies. In Arabic texts, the word is translated as ākhidhu al-Nujūm (
Arabic: آخِذُ ٱلنُّجُومْ,
lit.'star-taker'), a direct translation of the Greek word.[6]
Al-Biruni quotes and criticises medieval scientist
Hamza al-Isfahani who stated:[6] "asturlab is an arabisation of this Persian phrase" (sitara yab, meaning "taker of the stars").[7] In
medieval Islamic sources, there is also a
folk etymology of the word as "lines of lab", where "Lab" refers to a certain son of
Idris (
Enoch). This etymology is mentioned by a 10th-century scientist named
al-Qummi but rejected by
al-Khwarizmi.[8]
History
Ancient world
An early astrolabe was invented in the
Hellenistic civilization by
Apollonius of Perga between 220 and 150 BC, often attributed to
Hipparchus. The astrolabe was a marriage of the
planisphere and
dioptra, effectively an analog calculator capable of working out several different kinds of problems in astronomy. Another related device, used for similar purposes in the ancient world, is the
armillary sphere.
Theon of Alexandria (
c. 335 –
c. 405) wrote a detailed treatise on the astrolabe, and Lewis[9] argues that
Ptolemy used an astrolabe to make the astronomical observations recorded in the Tetrabiblos. The invention of the plane astrolabe is sometimes wrongly attributed to Theon's daughter
Hypatia (
c. 350–370; died AD 415),[10][11][12][13] but it's known to have been used at least 500 years earlier.[11][12][13] The misattribution comes from a misinterpretation of a statement in a letter written by Hypatia's pupil
Synesius (
c. 373 –
c. 414),[11][12][13] which mentions that Hypatia had taught him how to construct a plane astrolabe, but does not say that she invented it.[11][12][13]
Astrolabes continued in use in the Greek-speaking world throughout the
Byzantine period. About AD 550, Christian philosopher
John Philoponus wrote a treatise on the astrolabe in Greek, which is the earliest extant treatise on the instrument.[a] Mesopotamian bishop
Severus Sebokht also wrote a treatise on the astrolabe in the
Syriac language in the mid-7th century.[b] Sebokht refers to the astrolabe as being made of brass in the introduction of his treatise, indicating that metal astrolabes were known in the Christian East well before they were developed in the Islamic world or in the Latin West.[14]
The first Renaissance treatises dealing with scientific problems were based on earlier classical works and were often concerned with Ptolemaic doctrines.[citation needed]
The mathematical background was established by Muslim astronomer
Albatenius in his treatise Kitab az-Zij (c. AD 920), which was translated into Latin by
Plato Tiburtinus (De Motu Stellarum). The earliest surviving astrolabe is dated
AH 315 (AD 927–928). In the Islamic world, astrolabes were used to find the times of sunrise and the rising of fixed stars, to help schedule morning prayers (
salat). In the 10th century,
al-Sufi first described over 1,000 different uses of an astrolabe, in areas as diverse as
astronomy,
astrology,
navigation,
surveying, timekeeping, prayer,
Salat,
Qibla, etc.[18][19]
The
spherical astrolabe was a variation of both the astrolabe and the
armillary sphere, invented during the
Middle Ages by astronomers and
inventors in the Islamic world.[c] The earliest description of the spherical astrolabe dates to
Al-Nayrizi (
fl. 892–902). In the 12th century,
Sharaf al-Dīn al-Tūsī invented the linear astrolabe, sometimes called the "staff of al-Tusi", which was "a simple wooden rod with graduated markings but without sights. It was furnished with a plumb line and a double chord for making angular measurements and bore a perforated pointer".[20] The geared mechanical astrolabe was invented by Abi Bakr of
Isfahan in 1235.[21]
The first known metal astrolabe in Western Europe is the Destombes astrolabe made from brass in the eleventh century in Portugal.[22][23] Metal astrolabes avoided the warping that large wooden ones were prone to, allowing the construction of larger and therefore more accurate instruments. Metal astrolabes were heavier than wooden instruments of the same size, making it difficult to use them in navigation.[24]
Herman Contractus of
Reichenau Abbey, examined the use of the astrolabe in Mensura Astrolai during the 11th century.[25]Peter of Maricourt wrote a treatise on the construction and use of a universal astrolabe in the last half of the 13th century entitled Nova compositio astrolabii particularis. Universal astrolabes can be found at the History of Science Museum in Oxford.[26] David A. King, historian of Islamic instrumentation, describes the universal astrolobe designed by Ibn al-Sarraj of
Aleppo (aka Ahmad bin Abi Bakr; fl. 1328) as "the most sophisticated astronomical instrument from the entire Medieval and Renaissance periods".[27]
English author
Geoffrey Chaucer (c. 1343–1400) compiled A Treatise on the Astrolabe for his son, mainly based on a work by
Messahalla or
Ibn al-Saffar.[28][29] The same source was translated by French astronomer and astrologer Pélerin de Prusse and others. The first printed book on the astrolabe was Composition and Use of Astrolabe by
Christian of Prachatice, also using Messahalla, but relatively original.
In 1370, the first Indian treatise on the astrolabe was written by the
Jain astronomer
Mahendra Suri, titled Yantrarāja.[30]
A simplified astrolabe, known as a balesilha, was used by sailors to get an accurate reading of latitude while at sea. The use of the balesilha was promoted by
Prince Henry (1394–1460) while navigating for Portugal.[31]
The astrolabe was almost certainly first brought north of the Pyrenees by Gerbert of Aurillac (future
Pope Sylvester II), where it was integrated into the
quadrivium at the school in Reims, France, sometime before the turn of the 11th century.[32] In the 15th century, French instrument maker Jean Fusoris (c. 1365–1436) also started remaking and selling astrolabes in his shop in
Paris, along with portable sundials and other popular scientific devices of the day.
Thirteen of his astrolabes survive to this day.[33] One more special example of craftsmanship in early 15th-century Europe is the astrolabe designed by Antonius de Pacento and made by Dominicus de Lanzano, dated 1420.[34]
In the 16th century,
Johannes Stöffler published Elucidatio fabricae ususque astrolabii, a manual of the construction and use of the astrolabe. Four identical 16th-century astrolabes made by
Georg Hartmann provide some of the earliest evidence for
batch production by
division of labor. In 1612, Greek painter
Ieremias Palladas incorporated a sophisticated astrolabe in his painting depicting Catherine of Alexandria. The painting was entitled Catherine of Alexandria and featured a device called the System of the Universe (Σύστημα τοῦ Παντός). The device featured the planets with the names in Greek:
Selene (Moon),
Hermes (Mercury),
Aphrodite (Venus),
Helios (Sun),
Ares (Mars),
Zeus (Jupiter), and
Chronos (Saturn). The device also featured celestial spheres following the Ptolemaic model and Earth was depicted as a blue sphere with circles of geographic coordinates. A complex line representing the axis of the Earth covered the entire instrument.[35]
Medieval astrolabes
A treatise explaining the importance of the astrolabe by
Nasir al-Din al-Tusi, Persian scientist
A page from the 1575 book "Astrolabium" depicting an astrolabe. Masha'Allah
Public Library Bruges [
nl] Ms. 522
Astrolabes and clocks
Mechanical
astronomical clocks were initially influenced by the astrolabe; they could be seen in many ways as clockwork astrolabes designed to produce a continual display of the current position of the sun, stars, and planets. For example,
Richard of Wallingford's clock (c. 1330) consisted essentially of a star map rotating behind a fixed rete, similar to that of an astrolabe.[36]
Many astronomical clocks use an astrolabe-style display, such as the famous
clock at Prague, adopting a stereographic projection (see below) of the ecliptic plane. In recent times, astrolabe watches have become popular. For example, Swiss watchmaker
Ludwig Oechslin designed and built an astrolabe wristwatch in conjunction with
Ulysse Nardin in 1985.[37] Dutch watchmaker Christaan van der Klauuw also manufactures astrolabe watches today.[38]
Above the mater and tympan, the rete, a framework bearing a projection of the
ecliptic plane and several
pointers indicating the positions of the brightest
stars, is free to rotate. These pointers are often just simple points, but depending on the skill of the craftsman can be very elaborate and artistic. There are examples of astrolabes with artistic pointers in the shape of balls, stars, snakes, hands, dogs' heads, and leaves, among others.[39] The names of the indicated stars were often engraved on the pointers in Arabic or Latin.[40] Some astrolabes have a narrow rule or label which rotates over the rete, and may be marked with a scale of
declinations.
The rete, representing the
sky, functions as a
star chart. When it is rotated, the stars and the
ecliptic move over the projection of the coordinates on the tympan. One complete rotation corresponds to the passage of a day. The astrolabe is, therefore, a predecessor of the modern
planisphere.
On the back of the mater, there is often engraved a number of scales that are useful in the astrolabe's various applications. These vary from designer to designer, but might include curves for time conversions, a
calendar for converting the day of the month to the sun's position on the ecliptic, trigonometric scales, and graduation of 360 degrees around the back edge. The alidade is attached to the back face. An alidade can be seen in the lower right illustration of the Persian astrolabe above. When the astrolabe is held vertically, the alidade can be rotated and the sun or a star sighted along its length, so that its altitude in degrees can be read ("taken") from the graduated edge of the astrolabe; hence the word's Greek roots: "astron" (ἄστρον) = star + "lab-" (λαβ-) = to take. The alidade had vertical and horizontal cross-hairs which plots locations on an azimuthal ring called an almucantar (altitude-distance circle).
An arm called a radius connects from the center of the astrolabe to the optical axis which is parallel with another arm also called a radius. The other radius contains graduations of altitude and distance measurements.
A shadow square also appears on the back of some astrolabes, developed by Muslim astrologists in the 9th Century, whereas devices of the Ancient Greek tradition featured only altitude scales on the back of the devices.[41] This was used to convert shadow lengths and the altitude of the sun, the uses of which were various from surveying to measuring inaccessible heights.[42]
Devices were usually signed by their maker with an inscription appearing on the back of the astrolabe, and if there was a patron of the object, their name would appear inscribed on the front, or in some cases, the name of the reigning sultan or the teacher of the astrolabist has also been found to appear inscribed in this place.[43] The date of the astrolabe's construction was often also signed, which has allowed historians to determine that these devices are the second oldest scientific instrument in the world. The inscriptions on astrolabes also allowed historians to conclude that astronomers tended to make their own astrolabes, but that many were also made to order and kept in stock to sell, suggesting there was some contemporary market for the devices.[43]
Construction of astrolabes
The
Hartmann astrolabe in
Yale collection. This instrument shows its rete and rule.
Celestial Globe, Isfahan (?), Iran 1144. Shown at the
Louvre Museum, this globe is the third oldest surviving in the world.
Computer-generated planispheric astrolabe
Mathematical basis
The construction and design of astrolabes are based on the application of the
stereographic projection of the
celestial sphere. The point from which the projection is usually made is the
South Pole. The plane onto which the projection is made is that of the
Equator.[44]
Designing a tympanum through stereographic projection
The tympanum captures the celestial coordinate axes upon which the rete will rotate. It is the component that will enable the precise determination of a star's position at a specific time of
day and
year.
Therefore, it should project:
The
zenith, which will vary depending on the
latitude of the astrolabe user.
The
horizon line and
almucantar or circles parallel to the horizon, which will allow for the determination of a celestial body's
altitude (from the horizon to the zenith).
The
celestial meridian (north-south meridian, passing through the zenith) and secondary meridians (circles intersecting the north-south meridian at the zenith), which will enable the measurement of
azimuth for a celestial body.
When projecting onto the celestial equatorial plane, three concentric circles correspond to the celestial sphere's three
circles of latitude (left side of the image). The largest of these, the projection on the celestial equatorial plane of the celestial
Tropic of Capricorn, defines the size of the astrolabe's tympanum. The center of the tympanum (and the center of the three circles) is actually the north-south axis around which Earth rotates, and therefore, the rete of the astrolabe will rotate around this point as the hours of the day pass (due to
Earth's rotational motion).
The three concentric circles on the tympanum are useful for determining the exact moments of
solstices and
equinoxes throughout the year: if the sun's altitude at noon on the rete is known and coincides with the outer circle of the tympanum (Tropic of Capricorn), it signifies the
winter solstice (the sun will be at the
zenith for an observer at the Tropic of Capricorn, meaning summer in the southern hemisphere and winter in the northern hemisphere). If, on the other hand, its altitude coincides with the inner circle (Tropic of Cancer), it indicates the
summer solstice. If its altitude is on the middle circle (equator), it corresponds to one of the two
equinoxes.
The horizon and the measurement of altitude
On the right side of the image above:
The blue arrow indicates the direction of true north (the
North Star).
The central blue point represents Earth (the observer's location).
The black arrow represents the
zenith direction for the observer (which would vary depending on the observer's
latitude).
The two black circles represent the
horizon surrounding the observer, which is perpendicular to the zenith vector and defines the portion of the
celestial sphere visible to the observer, and its projection on the celestial equatorial plane.
The geographic south of the celestial sphere acts as the
projection pole.
When projecting the
horizon onto the celestial equatorial plane, it transforms into an ellipse upward-shifted relatively to the center of the tympanum (both the observer and the projection of the north-south axis). This implies that a portion of the celestial sphere will fall outside the outer circle of the tympanum (the projection of the celestial
Tropic of Capricorn) and, therefore, won't be represented.
Additionally, when drawing circles parallel to the horizon up to the zenith (
almucantar), and projecting them on the celestial equatorial plane, as in the image above, a grid of consecutive ellipses is constructed, allowing for the determination of a
star's altitude when its rete overlaps with the designed tympanum.
The meridians and the measurement of azimuth
On the right side of the image above:
The blue arrow indicates the direction of true north (the
North Star).
The central blue point represents Earth (the observer's location).
The black arrow represents the
zenith direction for the observer (which would vary depending on the observer's
latitude).
The two black circles represent the
horizon surrounding the observer, which is perpendicular to the zenith vector and defines the portion of the
celestial sphere visible to the observer, and its projection on the celestial equatorial plane.
The five red dots represent the
zenith, the
nadir (the point on the
celestial sphere opposite the zenith with respect to the observer), their projections on the celestial equatorial plane, and the center (with no physical meaning attached) of the circle obtained by projecting the secondary meridian (see below) on the celestial equatorial plane.
The orange circle represents the
celestial meridian (or meridian that goes, for the observer, from the north of the horizon to the south of the horizon passing through the zenith).
The two red circles represent a secondary meridian with an
azimuth of 40° East relative to the observer's horizon (which, like all secondary meridians, intersects the principal meridian at the zenith and nadir), and its projection on the celestial equatorial plane.
The geographic south of the celestial sphere acts as the
projection pole.
When projecting the
celestial meridian, it results in a straight line that overlaps with the vertical axis of the tympanum, where the
zenith and
nadir are located. However, when projecting the 40° E meridian, another circle is obtained that passes through both the zenith and nadir projections, so its center is located on the perpendicular
bisection of the segment connecting both points. In deed, the projection of the celestial meridian can be considered as a circle with an infinite radius (a straight line) whose center is on this bisection and at an infinite distance from these two points.
If successive meridians that divide the celestial sphere into equal sectors (like "orange slices" radiating from the zenith) are projected, a family of curves passing through the zenith projection on the tympanum is obtained. These curves, once overlaid with the rete containing the major stars, allow for determining the
azimuth of a star located on the rete and rotated for a specific time of day.
^Modern editions of
John Philoponus' treatise on the astrolabe are De usu astrolabii eiusque constructione libellus (On the Use and Construction of the Astrolabe), ed. Heinrich Hase, Bonn: E. Weber, 1839,
OCLC165707441 (or id. Rheinisches Museum für Philologie 6 (1839): 127–71); repr. and translated into French by Alain Philippe Segonds, Jean Philopon, traité de l'astrolabe, Paris: Librairie Alain Brieux, 1981,
OCLC10467740; and translated into English by H.W. Green in R.T. Gunther, The Astrolabes of the World, Vol. 1/2, Oxford, 1932,
OL18840299M repr. London: Holland Press, 1976,
OL14132393M pp. 61–81.
^O'Leary, De Lacy (1948).
How Greek Science Passed to the Arabs. Routledge and Kegan Paul. "The most distinguished Syriac scholar of this later period was
Severus Sebokht (d. 666–7), Bishop of Kennesrin. [...] In addition to these works [...] he also wrote on astronomical subjects (Brit. Mus. Add. 14538), and composed a treatise on the astronomical instrument known as the astrolabe, which has been edited and published by F. Nau (Paris, 1899)." Severus' treatise was translated by Jessie Payne Smith Margoliouth in R.T. Gunther, Astrolabes of the World, Oxford, 1932, pp. 82–103.
^Savage-Smith, Emilie (1993). "Book Reviews". Journal of Islamic Studies. 4 (2): 296–299.
doi:
10.1093/jis/4.2.296. There is no evidence for the Hellenistic origin of the spherical astrolabe, but rather evidence so far available suggests that it may have been an early but distinctly Islamic development with no Greek antecedents.
^Nizamoglu, Cem (2005-08-10).
"Using an Astrolabe". Muslim Heritage. Retrieved 2023-10-16.
^Lachièz-Rey, Marc; Luminet, Jean-Pierre (2001). Celestial Treasury: From the Music of Spheres to the Conquest of Space. Translated by Joe Laredo. Cambridge, United Kingdom: Cambridge University Press. p. 74.
ISBN978-0-521-80040-2.
^"Introduction". The Astrolabe: an Online Resource. 2006. Retrieved 2020-05-15.
^Harley, J. B.; Woodward, David (1992). The history of cartography. Chicago, Illinois: University of Chicago Press. p. 31.
ISBN0-226-31635-1.
^Kunitzsch, Paul (1981). "On the authenticity of the treatise on the composition and use of the astrolabe ascribed to Messahalla". Archives Internationales d'Histoire des Sciences Oxford. 31 (106): 42–62.
^Ralf Kern (2010), Wissenschaftliche Instrumente in ihrer Zeit. Band 1: Vom Astrolab zum mathematischen Besteck. Cologne, S. 204.
ISBN978-3-86560-865-9
^
abStephenson, Bruce; Bolt, Marvin; Friedman, Anna Felicity (2000). The Universe Unveiled: Instruments and Images through History. Cambridge, UK: Cambridge University Press. pp. 108–109.
ISBN0-521-79143-X.
^King, David A. Some Medieval Astronomical Instruments and Their Secrets, in Mazzolini, R. G. (ed.), Non-Verbal Communication in Science prior to 1900.
Florence. p. 30.
^King, David A. (2018). The Astrolabe: What it is & what it is not. Frankfurt, Germany:
Frankfurt.
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King, D. A. (1981), "The Origin of the Astrolabe According to the Medieval Islamic Sources", Journal for the History of Arabic Science, 5: 43–83
King, Henry (1978), Geared to the Stars: the Evolution of Planetariums, Orreries, and Astronomical Clocks, University of Toronto Press
Krebs, Robert E.; Krebs, Carolyn A. (2003), Groundbreaking Scientific Experiments, Inventions, and Discoveries of the Ancient World, Greenwood Press.
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