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Astrolabe
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{{Short description|Astronomical instrument}}{{Hatnote group|{{For|other pages with a similar name|Astrolabe (disambiguation)}}{{Distinguish|Cosmolabe}}}}File:Khalili Collection Islamic Art sci 0430 back.jpg|alt=Planispheric Astrolabe made of brass, cast, with fretwork rete and surface engraving|thumb|upright=1.2|North African, 9th century AD, Planispheric Astrolabe. Khalili Collection. ]]File:Iranian Astrolabe 14.jpg|thumb|A modern astrolabe made in upright=1.2An astrolabe ( {{transliteration|grc|astrolábos}}, {{gloss|star-taker}}; {{transliteration|ar|al-Asá¹urlÄb}}; {{transliteration|fa|SetÄreyÄb}}) 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,NEWS, The New York Times,weblink HISTORIANS' HOME YIELDS RICH LODE; 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- the content below is remote from Wikipedia
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access-date=February 4, 2024, 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(File:Lot-stoffler-johannes-1452-1531-elucidatio-fabricae-usuque-astrolabii-6069643.jpg|thumb|upright=1.4|16th-century woodcut of measurement of a building's height with an astrolabe)A 10th-century astronomer Abd Al-Rahman Al-Sufi wrote a massive text of 386 chapters on the astrolabe. His worked described more than 1000 applications for the astrolabe's various functions,BOOK, Birx, H. James,weblink Encyclopedia of Time: Science, Philosophy, Theology, & Culture, 2009, SAGE, 978-1-4129-4164-8, 59, en, . These ranged from the astrological, the astronomical and the religious, to navigation and 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|date=March 2024}}EtymologyThe Oxford English Dictionary gives the translation "star-taker" for the English word astrolabe and traces it through medieval Latin to the Greek word ἀστÏολάβος : {{transliteration|grc|astrolábos}},WEB,weblink Astrolabe, Oxford English Dictionary, 2nd, 1989, WEB,weblinkweblink" title="web.archive.org/web/20131022193917weblink">weblink dead, October 22, 2013, Astrolabe, Oxford Dictionaries (website), Oxford Dictionaries, from ἄστÏον : {{transliteration|grc|astron}} "star" and λαμβάνειν : {{transliteration|grc|lambanein}} "to take".WEB,weblink Online Etymology Dictionary, Etymonline.com, 2013-11-07, In the medieval Islamic world the Arabic word {{transliteration|ar|al-AsturlÄb}} (i.e., astrolabe) was given various etymologies. In Arabic texts, the word is translated as {{transliteration|ar|Äkhidhu al-NujÅ«m}} (, {{lit|star-taker}}), a direct translation of the Greek word.{{sfn|King|1981|p=44}}Al-Biruni quotes and criticises medieval scientist Hamza al-Isfahani who stated:{{sfn|King| 1981|p= 44}} "asturlab is an arabisation of this Persian phrase" ({{transliteration|fa|sitara yab}}, meaning "taker of the stars").{{sfn|King|1981|p=51}} 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.{{sfn|King|1981|p=45}}HistoryAncient worldFile:Soluntum, Casa Leda, mosaic of an armillary sphere.jpg|thumb|upright=1.2|Armillary SphereJOURNAL, Berlin, Nicole, Mixed-Media Domestic Ensembles in Roman Sicily: The House of Leda at Soluntum, Arts, June 2019, 8, 2, 62, 10.3390/arts8020062, en, 2076-0752, free, JOURNAL, Westgate, Ruth, Pavimenta atque emblemata vermiculata: Regional Styles in Hellenistic Mosaic and the First Mosaics at Pompeii, American Journal of Archaeology, 2000, 104, 2, 255–275, 10.2307/507451, 507451, 194101486,weblink 0002-9114, mosaic from the Casa di Leada at Soluntum in SicilySicilyAn 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. The earliest known depiction of an astrolabe is a mosaic in the Casa di Leada at Soluntum in Sicily, which may have been imported from Alexandria in Egypt.{{Sfn|Wolf|2003|pp=64-69}}{{dubious|date=August 2023}}Theon of Alexandria ({{circa|335}} – {{circa|405}}) wrote a detailed treatise on the astrolabe, and Lewis{{sfn|Lewis|2001}} 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 ({{circa|350–370}}; died AD 415),Michael Deakin (August 3, 1997). "Ockham's Razor: Hypatia of Alexandria". ABC Radio. Retrieved July 10, 2014.BOOK, Theodore, Jonathan, 2016, The Modern Cultural Myth of the Decline and Fall of the Roman Empire,weblink Manchester, England, Palgrave, Macmillan, 183, 978-1-137-56997-4, BOOK, Deakin, Michael A. B., 2007, Hypatia of Alexandria: Mathematician and Martyr,weblink Amherst, New York, Prometheus Books, 102–104, 978-1-59102-520-7, BOOK, Bradley, Michael John, 2006, The Birth of Mathematics: Ancient Times to 1300,weblink New York City, New York, Infobase Publishing, 63, 9780816054237, but it's known to have been used at least 500 years earlier. The misattribution comes from a misinterpretation of a statement in a letter written by Hypatia's pupil Synesius ({{circa|373}} – {{circa|414}}), which mentions that Hypatia had taught him how to construct a plane astrolabe, but does not say that she invented it.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.{{efn|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, {{OCLC|165707441}} (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, {{OCLC|10467740}}; and translated into English by H.W. Green in R.T. Gunther, The Astrolabes of the World, Vol. 1/2, Oxford, 1932, {{OL|18840299M}} repr. London: Holland Press, 1976, {{OL|14132393M }} pp. 61–81.}} Mesopotamian bishop Severus Sebokht also wrote a treatise on the astrolabe in the Syriac language in the mid-7th century.{{efn|BOOK, Routledge and Kegan Paul, O'Leary, De Lacy, De Lacy O'Leary, How Greek Science Passed to the Arabs, 1948,weblink "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.}} 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.WEB, Severus, Sebokht, Description of the astrolabe,weblink Tertullian.org, The first Renaissance treatises dealing with scientific problems were based on earlier classical works and were often concerned with Ptolemaic doctrines.{{citation needed|date=March 2022}}Medieval eraAstrolabes were further developed in the medieval Islamic world, where Muslim astronomers introduced angular scales to the design,See p. 289 of {{Citation | issn = 1475-4878 | issue = 5 | last = Martin | title = Surveying and navigational instruments from the historical standpoint | date = 1923 | bibcode = 1923TrOS...24..289M }} adding circles indicating azimuths on the horizon.{{citation | editor-first=Victor J. | first=J. Lennart | chapter=Mathematics in Medieval Islam | publisher=Princeton University Press | isbn=978-0-691-11485-9 | Geography in medieval Islam>aid to navigation and as a way of finding the Qibla, the direction of Mecca. Eighth-century mathematician Muhammad al-Fazari is the first person credited with building the astrolabe in the Islamic world.Richard Nelson Frye: Golden Age of Persia. p. 163The 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.WEB, Nizamoglu, Cem, 2005-08-10, Using an Astrolabe,weblink 2023-10-16, Muslim Heritage, BOOK, Lachièz-Rey, Marc, Celestial Treasury: From the Music of Spheres to the Conquest of Space, Luminet, Jean-Pierre, 2001, Cambridge University Press, Translated by Joe Laredo, 978-0-521-80040-2, Cambridge, United Kingdom, 74, en, (File:Astrolabium.jpg|thumb|An Arab astrolabe from 1208)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.{{efn|JOURNAL, Emilie, Savage-Smith, Emilie Savage-Smith, 1993, Book Reviews, Journal of Islamic Studies, 4, 2, 296–299, 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., }} The earliest description of the spherical astrolabe dates to Al-Nayrizi (fl. 892–902). In the 12th century, Sharaf al-DÄ«n al-TÅ«sÄ« 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".{{MacTutor|id=Al-Tusi_Sharaf|title=Sharaf al-Din al-Muzaffar al-Tusi}} The geared mechanical astrolabe was invented by Abi Bakr of Isfahan in 1235.JOURNAL, Silvio Bedini, Silvio A., Bedini, Francis Maddison, Francis R., Maddison, 1966, Mechanical Universe: The Astrarium of Giovanni de' Dondi, Transactions of the American Philosophical Society, 56, 5, 1–69, 1006002, 10.2307/1006002, The first known metal astrolabe in Western Europe is the Destombes astrolabe made from brass in the eleventh century in Portugal.WEB,weblink Qantara – 'Carolingian' astrolabe, Qantara-med.org, 2013-11-07, Nancy Marie Brown (2010), "The Abacus and the Cross". p. 140. Basic Books. {{ISBN|978-0-465-00950-3}} 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.BOOK, Toward the Setting Sun: Columbus, Cabot, Vespucci, and the Race for America, David, Boyle, Bloomsbury Publishing USA, 2011, 9780802779786, 253,weblink .(File:Spherical astrolabe.jpg|thumb|Spherical astrolabe)Herman Contractus of Reichenau Abbey, examined the use of the astrolabe in Mensura Astrolai during the 11th century.BOOK,weblink Encyclopedia of world trade: from ancient times to the present, Routledge, 2015, 978-0765680587, Northrup, Cynthia Clark, Enhanced Credo, Armonk, New York, 72, en-us, 889717964, 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.WEB, Introduction,weblink 2006, The Astrolabe: an Online Resource, 2020-05-15, 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".BOOK, Harley, J. B., The history of cartography, Woodward, David, 1992, University of Chicago Press, 0-226-31635-1, Chicago, Illinois, 31, en-us, 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.JOURNAL, 31, 106, 42–62, Kunitzsch, Paul, On the authenticity of the treatise on the composition and use of the astrolabe ascribed to Messahalla, Archives Internationales d'Histoire des Sciences Oxford, 1981, BOOK, Springer Science & Business Media, 978-1-4020-4559-2, Selin, Helaine, Encyclopaedia of the History of Science, Technology, and Medicine in Non-Western Cultures,weblink limited, 2008-03-12, 1335, 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., 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 oSpherical astrolaberiginal.In 1370, the first Indian treatise on the astrolabe was written by the Jain astronomer Mahendra Suri, titled YantrarÄja.{{Citation | editor1-first=Thomas|editor1-last=Glick|editor2-first=Steven J.|editor2-last=Livesey|editor3-first=Faith|editor3-last=Wallis | title = Medieval Science, Technology, and Medicine: An Encyclopedia | date = 2005 | publisher = Routledge | isbn = 0-415-96930-1 | page = 464 | display-editors = 1 | url=https://books.google.com/books?id=SaJlbWK_-FcC&pg=PA464 }}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.BOOK, Encyclopedia of world trade : from ancient times to the present, Routledge, Northrup, Cynthia Clark, 2015, 978-0765680587, [Enhanced Credo edition], Armonk, New York, 460, 889717964,weblink 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.Nancy Marie Brown (2010), "The Abacus and the Cross". p. 143. basic Books. {{ISBN|978-0-465-00950-3}} 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.File:Detail of Astronomical Instrument Ieremias Palladas.png|thumb|upright=1|left|Astronomical Instrument Detail by Ieremias PalladasIeremias Palladas Thirteen of his astrolabes survive to this day.BOOK, The Biographical Encyclopedia of Astronomers, Hockey, Thomas, 2009, Springer Publishing, 978-0-387-31022-0, August 22, 2012,weblink 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.Ralf Kern (2010), Wissenschaftliche Instrumente in ihrer Zeit. Band 1: Vom Astrolab zum mathematischen Besteck. Cologne, S. 204. {{ISBN|978-3-86560-865-9}}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 (ΣÏστημα 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.JOURNAL, Vafea, Flora, 2017, The Astronomical Instruments in Saint Catherine's Iconography at the Holy Monastery of Sinai The Almagest Volume 8, Issue 2, Almagest, 8, 2,weblink Paris, University of Paris, 87, 10.1484/J.ALMAGEST.5.114932, {{Gallery|title=Medieval astrolabes|align=center | A treatise explaining the importance of the astrolabe by Nasir al-Din al-Tusi, Persian scientist | Astrolabe of Jean Fusoris, made in Paris, 1400 | An 18th-century Persian astrolabe | Disassembled 18th-century astrolabe | Exploded view of an astrolabe | Animation showing how celestial coordinate system | and geographic coordinate system>geographic coordinates are mapped on an astrolabe's tympan through a stereographic projection. Hypothetical tympan (40th parallel north | ) of a 16th-century European planisphere>planispheric astrolabe. | Astrolabe manual from the Alfonso X of Castile work Libros del saber de astronomÃa, 1276. | A page from the 1575 book "Astrolabium" depicting an astrolabe. Masha'Allah {{Interlanguage link multi | nl|3=Openbare Bibliotheek Brugge}} Ms. 522}}Astrolabes and clocksFile:Het gebruik van het astrolabium door Amerigo Vespucci, Jan Collaert II, Museum Plantin-Moretus, PK.OPB.0186.018.jpg|thumb|upright=1.4|Amerigo Vespucci observing the Southern Cross by looking over the top of an Armillary Sphere bizarrely held from the top like it's an astrolabe, however an astrolabe cannot be used by looking over the top of it. The page inexplicably contains the word "Astrolabium," by Jan Collaert II. Museum Plantin-Moretus, AntwerpAntwerpMechanical 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.{{sfn|North| 2005}}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 Dr. Ludwig Oechslin designed and built an astrolabe wristwatch in conjunction with Ulysse Nardin in 1985.WEB,weblink dead,weblink" title="web.archive.org/web/20110102024043weblink">weblink 2 January 2011, Astrolabium G. Galilei, Ulysse Nardin, Dutch watchmaker Christaan van der Klauuw also manufactures astrolabe watches today.WEB,weblink Christaan van der Klauuw,ConstructionAn astrolabe consists of a disk, called the mater (mother), which is deep enough to hold one or more flat plates called tympans, or climates. A tympan is made for a specific latitude and is engraved with a stereographic projection of circles denoting azimuth and altitude and representing the portion of the celestial sphere above the local horizon. The rim of the mater is typically graduated into hours of time, degrees of arc, or both.BOOK, Stephenson, Bruce, Marvin, Bolt, Anna Felicity, Friedman, The Universe Unveiled: Instruments and Images through History, 2000, Cambridge University Press, Cambridge, UK, 0-521-79143-X, 108–109, 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. The names of the indicated stars were often engraved on the pointers in Arabic or Latin.WEB,weblink Star Names on Astrolabes, Ian Ridpath, 2016-11-12, 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" (ἄστÏον) = 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.BOOK, King, David A., Some Medieval Astronomical Instruments and Their Secrets, in Mazzolini, R. G. (ed.), Non-Verbal Communication in Science prior to 1900, Florence, 30, 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.BOOK, King, David A., The Astrolabe: What it is & what it is not, Frankfurt, 2018, Frankfurt, Germany, 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.BOOK, Mayer, L. A., Islamic astrolabists and their works, A. Kunding, 1956, 1956iatw.book.....M, 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.{{Gallery|title=Construction of astrolabes|align=center | The Georg Hartmann | astrolabe in Yale University>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 basisThe 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.JOURNAL, Gentili, Graziano, Simonutti, Luisa, Struppa, Daniele C., The Mathematics of the Astrolabe and Its History,weblink Journal of Humanistic Mathematics, 2020, 10, 101–144, 10.5642/jhummath.202001.07, 211008813, free, 2158/1182616, free,Designing a tympanum through stereographic projection(File:Parts of a tympan of an astrolabe.png|thumb|upright=1.4|Parts of an Astrolabe tympanum)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 tropics and the equator define the tympanum(File:Proyección estereográfica de trópicos y ecuador en un astrolabio.png|thumb|upright=2.8|Stereographic projection of Earth's tropics and equator from the South Pole.)On the right side of the image above:
The horizon and the measurement of altitude(File:Proyección estereográfica del horizonte sobre el tÃmpano de un astrolabio.png|thumb|upright=2.8|Stereographic projection of an observer's horizon at a specific latitude)On the right side of the image above:
The meridians and the measurement of azimuth(File:Proyección estereográfica del horizonte y azimut sobre el tÃmpano de un astrolabio.png|thumb|upright=2.8|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:
See also
References
Bibliography
External links{{Commons and category|Astrolabe|Astrolabes}}{{EB1911 poster|Astrolabe}}{{Wiktionary|astrolabe}}
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