Thursday, January 1, 2015

Persian Astrolabe

What is a Persian Astrolabe?

The Persian Astrolabe is a historical astronomical instrument used by classical astronomers and astrologers. Brass astrolabes were developed in much of Persia (Iran), chiefly as an aid to navigation and as a way of finding the qibla, the direction of Mecca. In the Islamic world, astrolabes were used to find the times of sunrise and the rising of fixed stars, to help schedule morning prayers.

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It was the chief navigational instrument until the invention of the compass and sextant. Its many uses included locating and predicting the positions of the sun, moon, planets and stars; determining local time given the local longitude and vice-versa; surveying, and triangulation. Astrologers of European nations used astrolabes to construct horoscopes. In the Islamic world, they are and were used primarily for astronomical studies, though astrology was often involved there as well.

History


Ancient world

An early astrolabe was invented in the Hellenistic world in 150 BC and is often attributed to Hipparchus. A marriage of the planisphere and dioptra, the astrolabe was effectively an analog calculator capable of working out several different kinds of problems in spherical astronomy. Theon of Alexandria wrote a detailed treatise on the astrolabe, and Lewis (2001) argues that Ptolemy used an astrolabe to make the astronomical observations recorded in the Tetrabiblos.

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Astrolabes continued in use in the Greek-speaking world throughout the Byzantine period. About 550 AD the Christian philosopher John Philoponus wrote a treatise on the astrolabe in Greek, which is the earliest extant Greek treatise on the instrument. In addition, Severus Sebokht, a bishop who lived in Mesopotamia, also wrote a treatise on the astrolabe in Syriac in the mid-7th century. Severus Sebokht refers in the introduction of his treatise to the astrolabe as being made of brass, indicating that metal astrolabes were known in the Christian East well before they were developed in the Islamic world or the Latin West.

Medieval era

Astrolabes were further developed in the medieval Islamic world, where Muslim astronomers introduced angular scales to the astrolabe, adding circles indicating azimuths on the horizon.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 the astrolabe in the Islamic world is reportedly the 8th-century mathematician Muhammad al-Fazari.The mathematical background was established by the Muslim astronomer Albatenius in his treatise Kitab az-Zij (ca. 920 AD), which was translated into Latin by Plato Tiburtinus (De Motu Stellarum). The earliest surviving dated astrolabe is dated AH 315 (927/8 AD). 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, Salat, Qibla, etc.

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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. 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." The first geared mechanical astrolabe was later invented by Abi Bakr of Isfahan in 1235.

Peter of Maricourt, in the last half of the 13th century, also wrote a treatise on the construction and use of a universal astrolabe (Nova compositio astrolabii particularis). Universal astrolabes can be found at the History of Science Museum in Oxford.The English author Geoffrey Chaucer (ca. 1343–1400) compiled a treatise on the astrolabe for his son, mainly based on Messahalla. The same source was translated by the 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.

Astrolab

The first known metal astrolabe in Western Europe is the Destombes astrolabe made from brass in tenth-century Spain.Metal astrolabes avoided the warping that large wooden astrolabes were prone to, allowing the construction of larger and therefore more accurate instruments; however, metal astrolabes were also heavier than wooden instruments of the same size, making it difficult to use them as navigational instruments. 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. In the 15th century, the French instrument-maker Jean Fusoris (fr) (ca. 1365–1436) also started selling astrolabes in his shop in Paris, along with portable sundials and other popular scientific gadgets of the day. Thirteen of his astrolabes survive to this day.Finally, one more special example of craftsmanship in the early 15th-century Europe is the astrolabe dated 1420, designed by Antonius de Pacento and made by Dominicus de Lanzano.

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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.

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