The astrolabe, which is a precursor to thesextant,[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, themariner's astrolabe was developed to solve that problem.
16th-century woodcut of the measurement of a building's height with an astrolabe
The 10th centuryastronomerʿAbd al-Raḥmān al-Ṣūfī wrote a massive text of 386 chapters on the astrolabe, which reportedly described more than 1,000 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 theqibla, the direction ofMecca towards which Muslims must pray, could also be determined by this device. In addition to this, thelunar 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 asRamadan.[citation needed]
TheOxford English Dictionary gives the translation "star-taker" for the English wordastrolabe and traces it through medieval Latin to theGreek wordἀστρολάβος:astrolábos,[3][4]fromἄστρον:astron "star", andλαμβάνειν:lambanein "to take".[5]
In chapter 5.1 of theAlmagest, Ptolemy describes the construction of anarmillary sphere, and it is usually assumed that this was the instrument he used.
The mathematical background was established by Muslim astronomerAlbatenius in his treatiseKitab az-Zij(c. 920CE), which was translated into Latin byPlato Tiburtinus (De Motu Stellarum). The earliest surviving astrolabe is datedAH 315(927–928CE). 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 asastronomy,astrology,navigation,surveying, timekeeping, prayer,Salat,Qibla, etc.[22][23]
An Arab astrolabe from 1208
Thespherical astrolabe was a variation of both the astrolabe and thearmillary sphere, invented during theMiddle Ages by astronomers andinventors in the Islamic world.[b]The earliest description of the spherical astrolabe dates toAl-Nayrizi (fl. 892–902). In the 12th century,Sharaf al-Dīn al-Tūsī invented thelinear 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".[25] The geared mechanical astrolabe was invented by Abi Bakr ofIsfahan in 1235.[26]
The first known metal astrolabe in Western Europe is theDestombes astrolabe made from brass in the eleventh century in Portugal.[27][28](p 140) 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.[29]
Herman Contractus ofReichenau Abbey, examined the use of the astrolabe inMensura Astrolai during the 11th century.[30](p 72)Peter of Maricourt wrote a treatise on the construction and use of a universal astrolabe in the last half of the 13th century entitledNova compositio astrolabii particularis. Universal astrolabes can be found at theHistory of Science Museum, Oxford.[31] David A. King, historian of Islamic instrumentation, describes the universal astrolobe designed by Ibn al-Sarraj ofAleppo (a.k.a. Ahmad bin Abi Bakr; fl. 1328) as "the most sophisticated astronomical instrument from the entire Medieval and Renaissance periods".[32]
Front of a Gujaratiastrolabe, calibrated for Jodhpur, dated April 1644, and made for a Manirama, by an unknown artisan.
In 1370, the first Indian treatise on the astrolabe was written by theJain astronomerMahendra Suri, titledYantrarāja.[35]
A simplified astrolabe, known as abalesilha, was used by sailors to get an accurate reading of latitude while at sea. The use of thebalesilha was promoted byPrince Henry (1394–1460) while navigating for Portugal.[30](p 460)
The astrolabe was almost certainly first brought north of the Pyrenees by Gerbert of Aurillac (futurePope Sylvester II), where it was integrated into thequadrivium at the school in Reims, France, sometime before the turn of the 11th century.[28](p 143) In the 15th century, French instrument maker Jean Fusoris (c. 1365–1436) also started remaking and selling astrolabes in his shop inParis, along with portable sundials and other popular scientific devices of the day.
Thirteen of his astrolabes survive to this day.[36] 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.[37]
In the 16th century,Johannes Stöffler publishedElucidatio fabricae ususque astrolabii, a manual of the construction and use of the astrolabe. Four identical 16th century astrolabes made byGeorg Hartmann provide some of the earliest evidence forbatch production bydivision of labor.
Greek painterIeremias Palladas incorporated a sophisticated astrolabe in his 1612 painting depictingCatherine of Alexandria. The painting, entitledCatherine of Alexandria; in addition to the saint, showed a device labelled the 'system of the universe' (Σύστημα τοῦ Παντός). The device featured theclassical planets with their Greek names:Helios (Sun),Selene (Moon),Hermes (Mercury),Aphrodite (Venus),Ares (Mars),Zeus (Jupiter), andCronos (Saturn). The depicted device also had celestial spheres, following thePtolemaic model, and Earth was shown as a blue sphere with circles of geographic coordinates. A complicated line representing the axis of the Earth covered the entire instrument.[38]
Medieval
A treatise explaining the importance of the astrolabe byNasir al-Din al-Tusi, Persian scientist
Many astronomical clocks use an astrolabe-style display, such as the famousclock at Prague, adopting a stereographic projection (see below) of the ecliptic plane. In recent times, astrolabe watches have become popular. For example, Swiss watchmakerLudwig Oechslin designed and built an astrolabe wristwatch in conjunction withUlysse Nardin in 1985.[40] Dutch watchmaker Christaan van der Klauuw also manufactures astrolabe watches today.[41]
Above the mater and tympan, therete, a framework bearing a projection of theecliptic plane and severalpointers indicating the positions of the brighteststars, 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.[42] The names of the indicated stars were often engraved on the pointers in Arabic or Latin.[43] Some astrolabes have a narrowrule orlabel which rotates over the rete, and may be marked with a scale ofdeclinations.
The rete, representing thesky, functions as astar chart. When it is rotated, the stars and theecliptic 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 modernplanisphere.
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, acalendar 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. Thealidade 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.[44] 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.[45]
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.[46] 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.[46]
Construction of astrolabes
TheHartmann astrolabe inYale collection. This instrument shows its rete and rule.
Celestial Globe, Isfahan (?), Iran 1144. Shown at theLouvre Museum, this globe is the third oldest surviving in the world.
The construction and design of astrolabes are based on the application of thestereographic projection of thecelestial sphere. The point from which the projection is usually made is theSouth Pole. The plane onto which the projection is made is that of theEquator.[47]
Designing a tympanum through stereographic projection
The tympanum captures the celestial coordinate axes upon which therete will rotate. It is the component that will enable the precise determination of a star's position at a specific time ofday andyear.
Therefore, it should project:
Thezenith, which will vary depending on thelatitude of the astrolabe user.
Thehorizon line andalmucantar or circles parallel to the horizon, which will allow for the determination of a celestial body'saltitude (from the horizon to the zenith).
Thecelestial 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 ofazimuth for a celestial body.
When projecting onto the celestial equatorial plane, three concentric circles correspond to the celestial sphere's threecircles of latitude (left side of the image). The largest of these, the projection on the celestial equatorial plane of the celestialTropic 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, therete of the astrolabe will rotate around this point as the hours of the day pass (due toEarth's rotational motion).
The three concentric circles on the tympanum are useful for determining the exact moments ofsolstices andequinoxes throughout the year: if the sun's altitude at noon on therete is known and coincides with the outer circle of the tympanum (Tropic of Capricorn), it signifies thewinter solstice (the sun will be at thezenith 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 thesummer solstice. If its altitude is on the middle circle (equator), it corresponds to one of the twoequinoxes.
Stereographic projection of an observer's horizon at a specific latitude
On the right side of the image above:
The blue arrow indicates the direction of true north (theNorth Star).
The central blue point represents Earth (the observer's location).
The black arrow represents thezenith direction for the observer (which would vary depending on the observer'slatitude).
The two black circles represent thehorizon surrounding the observer, which is perpendicular to the zenith vector and defines the portion of thecelestial sphere visible to the observer, and its projection on the celestial equatorial plane.
The geographic south of the celestial sphere acts as theprojection pole.
When projecting thehorizon 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 celestialTropic of Capricorn) and, therefore, won't be represented.
Stereographic projection of the horizon and an almucantar.
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 astar's altitude when itsrete overlaps with the designed tympanum.
Stereographic projection of the north-south meridian and a meridian 40° E on the tympanum of an astrolabe
On the right side of the image above:
The blue arrow indicates the direction of true north (theNorth Star).
The central blue point represents Earth (the observer's location).
The black arrow represents thezenith direction for the observer (which would vary depending on the observer'slatitude).
The two black circles represent thehorizon surrounding the observer, which is perpendicular to the zenith vector and defines the portion of thecelestial sphere visible to the observer, and its projection on the celestial equatorial plane.
The five red dots represent thezenith, thenadir (the point on thecelestial 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 thecelestial 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 anazimuth 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 theprojection pole.
When projecting thecelestial meridian, it results in a straight line that overlaps with the vertical axis of the tympanum, where thezenith andnadir 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 perpendicularbisection 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 therete containing the major stars, allow for determining theazimuth of a star located on therete and rotated for a specific time of day.
Basic astrolabe, showing the guide stars and the method for locating the Sun.
^"The most distinguished Syriac scholar of this later period wasSeverus Sebokht (d. 666–667), 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)."[16]
^"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."[24]
^"Paul Kunitzsch has recently established that the Latin treatise on the astrolabe long ascribed to Ma'sh'allah and translated by John of Seville is in fact by Ibn al-Saffar, a disciple of Maslama al-Majriti."[34]
^"Historians' home yields rich lode".The New York Times. 18 May 1964. Retrieved4 February 2024.New York Society searches its own building for items to mark anniversary; show opens Thursday; portrait of Stuyvesant and Champlain's astrolabe will be on display.
^Nizamoglu, Cem (10 August 2005)."Using an astrolabe".Muslim Heritage (muslimheritage.com). Retrieved16 October 2023.
^Lachièz-Rey, Marc; Luminet, Jean-Pierre (2001).Celestial Treasury: From the music of spheres to the conquest of space. Translated by Laredo, Joe. Cambridge, UK: Cambridge University Press. p. 74.ISBN978-0-521-80040-2.
^Harley, J.B.; Woodward, David (1992).The History of Cartography. Chicago, IL: 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.
^Kern, Ralf (2010).Wissenschaftliche Instrumente in ihrer Zeit [Scientific Instruments in their Era] (in German). Vol. 1: Vom Astrolab zum mathematischen Besteck [From the astroabe to mathematical instruments]. Köln, DE: König. p. 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
Stöffler, Johannes (2007) [First published 1513],Stoeffler's Elucidatio – The Construction and Use of the Astrolabe [Elucidatio Fabricae Ususque Astrolabii], translated by Gunella, Alessandro; Lamprey, John, John Lamprey,ISBN978-1-4243-3502-2
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,ISBN978-0-8020-2312-4
Krebs, Robert E.; Krebs, Carolyn A. (2003),Groundbreaking Scientific Experiments, Inventions, and Discoveries of the Ancient World, Greenwood Press,ISBN978-0-313-31342-4
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 ofPractique 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,ISBN978-0-511-48303-5
North, John David (2005),God's Clockmaker: Richard of Wallingford and the Invention of Time, Continuum International Publishing Group,ISBN978-1-85285-451-5
.jpg)
.jpg)
![A page from the 1575 book "Astrolabium" depicting an astrolabe according to the astronomer Masha'allah. Public Library Bruges [nl] Ms. 522](/image.pl?url=https%3a%2f%2fen.wikipedia.org%2f%2fupload.wikimedia.org%2fwikipedia%2fcommons%2fthumb%2fb%2fb6%2fAstrolabium_Masha%2527allah_Public_Library_Brugge_Ms._522.tif%2flossy-page1-85px-Astrolabium_Masha%2527allah_Public_Library_Brugge_Ms._522.tif.jpg&f=jpg&w=240)
