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An astrolabe[1] (Arabic: اسطرلاب asterlab, ostorlab) is a historical astronomical instrument used by classical astronomers, navigators, and astrologers. Its many uses include locating and predicting the positions of the Sun, Moon, planets, and stars; determining local time (given local latitude) and vice-versa; surveying; and triangulation.

In the medieval Islamic world, they were introduced by Arabs[2] and used primarily for astronomical studies, as well as in other areas as diverse as astrology, geography, navigation, Qibla, Salah prayers, surveying, and timekeeping. In the European nations, astrolabes were used to construct horoscopes, for astronomical studies, and for navigation.

There is often confusion between the astrolabe and the mariner's astrolabe. While the astrolabe could be useful for determining latitude on land, it was an awkward instrument for use on the heaving deck of a ship or in wind. The mariner's astrolabe was developed to address these issues.

HistoryEdit

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An early primitive astrolabe was known among several astronomers in Hellenistic Egypt. A marriage of the planisphere and dioptra, the astrolabe was apparently an analog calculator capable of working out several problems in astronomy. The Egyptian astronomer, Theon of Alexandria, wrote a treatise on such an astrolabe, and Lewis (2001) argues that the Egyptian astronomer Ptolemy used an astrolabe to make some of his astronomical observations recorded in the Tetrabiblos.[3]

About 550 AD, the Egyptian Christian philosopher John Philoponus wrote a treatise on the astrolabe in Greek, which is the earliest extant Greek treatise on the instrument.[4] In addition, the Syrian Christian scholar Severus Sebokht also wrote a treatise on an astrolabe in Syriac in the mid-seventh century.[5] Sebokht refers in the introduction of his treatise to the astrolabe as being made of brass, indicating that a metal astrolabe was known in the Middle East at the time.[6]

Islamic worldEdit

See also: Islamic astronomy

The development of astrolabes was advanced significantly in the medieval Islamic world, where Arabic astronomers introduced angular scales to the astrolabe,[7] adding circles indicating azimuths on the horizon.[8] 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. The first person credited with building a brass astrolabe in the Islamic era is the eighth century Islamic mathematician and astronomer, Muhammad al-Fazari.[9] The mathematical background was established by the Arab astronomer, Muhammad ibn Jābir al-Harrānī al-Battānī (Albatenius), in his treatise Kitab az-Zij (ca. 920 AD), which was translated into Latin by Plato Tiburtinus (De Motu Stellarum). The earliest surviving astrolabe is dated to 315 AH (927/8 AD) in Islamic Iraq. 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, horoscopes, navigation, surveying, timekeeping, prayer, Salah, Qibla, etc.[10]

Abū Ishāq Ibrāhīm al-Zarqālī (Arzachel) of Al-Andalus constructed the first universal astrolabe which, unlike its predecessors, did not depend on the latitude of the observer, and could be used from anywhere on the Earth. This instrument became known in Europe as the "Saphaea". The astrolabe was introduced to other parts of Western Europe via Al-Andalus in the 11th century.[11]

The spherical astrolabe, a variation of both the astrolabe and the armillary sphere, was invented during the Middle Ages by astronomers and inventors in the Islamic world.[12] The earliest description of the spherical astrolabe dates back 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."[13] The first geared mechanical astrolabe was later invented by Abi Bakr of Isfahan in 1235.[14]

IndiaEdit

In 1370, the first Indian treatise on the astrolabe was written by the Jain astronomer Mahendra Suri.[15]

EuropeEdit

Peter of Maricourt in the last half of the thirteenth century wrote a treatise on the construction and use of an Islamic universal astrolabe (Nova compositio astrolabii particularis). However, given the complicated nature of the instrument, it is highly unlikely that any were actually constructed; at least none survive.

The English author Geoffrey Chaucer (ca. 1343–1400) compiled a treatise on the astrolabe for his son, mainly based on the work of 9th century Persian astrologer Messahalla (Mashallah ibn Athari). The same source was translated by the French astronomer and astrologer Pelerin de Prusse and others. The earliest known printed book on the astrolabe was Composition and Use of Astrolabe by Cristannus de Prachaticz, also using Messahalla, but relatively original.

The first known metal astrolabe known in Western Europe was developed in the fifteenth century by Rabbi Abraham Zacuto in Lisbon. Metal astrolabes improved on the accuracy of their wooden precursors. In the fifteenth century, the French instrument-maker Jean Fusoris (ca. 1365–1436) also started selling astrolabes in his shop in Paris, along with portable sundials and other popular scientific gadgets of the day.

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.

Astrolabes and clocksEdit

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At first mechanical astronomical clocks were influenced by the astrolabe; in many ways they could be seen as clockwork astrolabes designed to produce a continual display of the current position of the sun, stars, and planets. Ibn al-Shatir constructed the earliest astrolabic clock in the early 14th century.[16] At around the same time, Richard of Wallingford's clock (c. 1330) consisted essentially of a star map rotating behind a fixed rete, similar to that of an astrolabe.[17]

Many astronomical clocks, such as the famous clock at Prague, use an astrolabe-style display, adopting a stereographic projection (see below) of the ecliptic plane.

In 1985 Swiss watchmaker Dr. Ludwig Oechslin designed and built an astrolabe wristwatch in conjunction with Ulysse Nardin.

ConstructionEdit

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An astrolabe consists of a fragile 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 circular lines of equal azimuth and altitude representing the portion of the celestial sphere which is above the local horizon. The rim of the mater is typically graduated into hours of time, or degrees of arc, or both. 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. 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, has the function of a star chart. When it is rotated, the stars and the ecliptic move over the projection of the coordinates on the tympan. A complete rotation represents the passage of one day. The astrolabe is therefore a predecessor of the modern planisphere.

On the back of the mater there will often be engraved a number of scales which are useful in the astrolabe's various applications; these will 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 a 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 Persion astrolabe above. When the astrolabe is held vertically, the alidade can be rotated and a star sighted along its length, so that the star's 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.

See alsoEdit

NotesEdit

  1. "astrolabe", Oxford English Dictionary 2nd ed. 1989
  2. How Greek Science Passed to the Arabs By De Lacy O'Leary First published 1949 Routledge & Kegan Paul Ltd. ISBN 0 7100 1903 3 Assyrian International News Agency Books Online read it here: http://www.aina.org/books/hgsptta.htm#ch6 The Arab conquest of 632 did not check the religious or intellectual life of either the Nestorian or Monophysite community. The Arabs exacted tribute, but so had the Persian and Roman governments. The tribute-paying communities were left free to follow their own laws, religion, and customs, and to lead their own discourse between Egypt, Persia, and Syria was easier than before, and this favoured intellectual culture which looked to Alexandria for guidance, though as Alexandria became immersed in commercial interests that guidance had to be sought in other cities which became its cultural heirs. The most distinguished Syriac scholar of this later period was Severus Sebokht (d. 666-7), Bishop of Kennesrin. He wrote letters on theological subjects to Basil of Cyprus and Sergius, abbot of Skiggar, as well as two discourses on St. Gregory Nazianzen. On Aristotelian logic he composed a treatise on the syllogisms in the Analytics of Aristotle, a commentary on the Hermeneutics which was based on the commentary of Paul the Persian, a letter to Aitilaha of Mosul on certain terms used in the Hermeneutics (Brit. Mus. Add. 17156), and a letter to the periodeutes Yaunan on the logic of Aristotle (Camb. Univ. Lib. Add. 2812). In addition to these works on logic 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). In all this he showed himself the product of Alexandrian science and illustrated the widening scientific interests of the period. It seems that he took steps towards introducing the Indian numerals, but this was not carried on by any immediate successor. His work represents the highest level reached by any Syriac scientist and this, it will be noted, was associated with Kennesrin.
  3. Evans (1998:155)
    Krebs & Krebs (2003:56)
  4. Modern editions of John Philoponus' treatise on the astrolabe are On the Use and Construction of the Astrolabe, ed. H. Hase, Bonn: E. Weber, 1839 (or id. Rheinisches Museum für Philologie 6 (1839): 127-71); repr. and translated into French by A.P. Segonds, Jean Philopon, traité de l'astrolabe, Paris: Librairie Alain Brieux, 1981; and translated into English by H.W. Green in R.T. Gunther, The Astrolabes of the World, Vol. 1/2, Oxford, 1932, repr. London: Holland Press, 1976, pp. 61-81.
  5. Severus' treatise was translated by Jessie Payne Smith Margoliouth in R.T. Gunther, Astrolabes of the world Oxford, 1932, p. 82-103.
  6. Severus Sebokht, Description of the astrolabe http://www.tertullian.org/fathers/severus_sebokht_astrolabe_01_trans.htm
  7. {{citation|title=Surveying and navigational instruments from the historical standpoint|author=L. C. Martin|year=1923|[[Optical Society of America|Transactions of the Optical Society|volume=24|pages=289-303 [289]|doi=10.1088/1475-4878/24/5/302}}
  8. Victor J. Katz & Annette Imhausen (2007), The mathematics of Egypt, Mesopotamia, China, India, and Islam: a sourcebook, Princeton University Press, p. 519, ISBN 0691114854 
  9. Richard Nelson Frye: Golden Age of Persia. p. 163
  10. Dr. Emily Winterburn (National Maritime Museum), Using an Astrolabe, Foundation for Science Technology and Civilisation, 2005.
  11. M. T. Houtsma and E. van Donzel (1993), E. J. Brill's First Encyclopaedia of Islam, Brill Publishers, ISBN 9004082654
  12. Emilie Savage-Smith (1993). "Book Reviews", Journal of Islamic Studies 4 (2), p. 296-299.
    "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."
  13. O'Connor, John J.; Robertson, Edmund F., "Sharaf al-Din al-Muzaffar al-Tusi", MacTutor History of Mathematics archive, University of St Andrews .
  14. Silvio A. Bedini, Francis R. Maddison (1966). "Mechanical Universe: The Astrarium of Giovanni de' Dondi", Transactions of the American Philosophical Society 56 (5), p. 1-69.
  15. Glick et al., eds. (2005). Medieval Science, Technology, and Medicine: An Encyclopedia. Routledge. pp. 464. ISBN 0415969301. 
  16. David A. King (1983). "The Astronomy of the Mamluks", Isis 74 (4), p. 531-555 [545-546].
  17. John David North, "God's Clockmaker: Richard of Wallingford and the Invention of Time", Continuum International Publishing Group, 2005, ISBN 978-1852854515

ReferencesEdit

  • Evans, James (1998), The History and Practice of Ancient Astronomy, Oxford University Press, ISBN 0195095391 .
  • Alessandro Gunella and John Lamprey, Stoeffler's Elucidatio (translation of Elucidatio fabricae ususque astrolabii into English). Published by John Lamprey, 2007. lamprey@frii.com
  • Krebs, Robert E.; Krebs, Carolyn A. (2003), Groundbreaking Scientific Experiments, Inventions, and Discoveries of the Ancient World, Greenwood Press .
  • Lewis, M. J. T. (2001), Surveying Instruments of Greece and Rome, Cambridge University Press .
  • John North. God's Clockmaker, Richard of Wallingford and the invention of time. Hambledon and London, 2006.
  • Critical edition of Pelerin de Prusse on the Astrolabe (translation of Practique de Astralabe). Editors Edgar Laird, Robert Fischer. Binghamton, New York, 1995, in Medieval & Renaissance Texts & Studies. ISBN 0-86698-132-2
  • King, Henry Geared to the Stars: the evolution of planetariums, orreries, and astronomical clocks University of Toronto Press, 1978

External linksEdit

Template:Islamic astronomy Template:Greek astronomy

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