Astrolabe

An astrolabe (Greek: ἀστρολάβος astrolabos; Arabic: ٱلأَسْطُرلابal-Asturlāb; Persian: اَختِرِیابAkhtaryab) is an elaborate inclinometer, historically used by astronomers and navigators to measure the inclined position in the sky of a celestial body, day or night. The word astrolabe means "the one that catches the heavenly bodies."[2] It can thus 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,[3] the European Middle Ages, and the Renaissance for all these purposes.

The astrolabe's importance not only comes from the early development of astronomy,[2] but is also 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.

OED gives the translation "star-taker" for the English word astrolabe and traces it through medieval Latin to the Greek word astrolabos,[4][5] from astron "star" and lambanein "to take".[6] 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 "ākhdhu al-Nujuum" (Arabic: آخِذُ ٱلنُّجُومْ‎, lit. "star-taker"), a direct translation of the Greek word.[7]

Al-Biruni quotes and criticizes medieval scientist Hamzah al-Isfahani who stated:[7] "asturlab is an arabization of this Persian phrase" (sitara yab, meaning "taker of the stars").[8] 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.[9]

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 spherical astronomy. Theon of Alexandria (c. 335 – c. 405) wrote a detailed treatise on the astrolabe, and Lewis[10] 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 415 AD),[11][12][13][14] but it is, in fact, known to have already been in use at least 500 years before Hypatia was born.[12][13][14] The misattribution comes from a misinterpretation of a statement in a letter written by Hypatia's pupil Synesius (c. 373 – c. 414),[12][13][14] which mentions that Hypatia had taught him how to construct a plane astrolabe, but does not state anything about her having invented it herself.[12][13][14]

Astrolabes continued in use in the Greek-speaking world throughout the Byzantine period. About 550 AD, 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.[15]

Astrolabes were further developed in the medieval Islamic world, where Muslim astronomers introduced angular scales to the design,[16] adding circles indicating azimuths on the horizon.[17] It was widely used throughout the Muslim world, chiefly as an 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.[18]

The mathematical background was established by Muslim astronomer Albatenius in his treatise Kitab az-Zij (c. 920 AD), which was translated into Latin by Plato Tiburtinus (De Motu Stellarum). The earliest surviving astrolabe is dated AH 315 (927–28 AD).[19] 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.[20][21]

This page was last edited on 9 July 2018, at 17:17 (UTC).
Reference: https://en.wikipedia.org/wiki/Astrolabe under CC BY-SA license.

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