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Shortly after 1424, Ulugh Beg’s catalog had slightly less than the number of stars in Ptolemy’s 2nd century catalog, but was slightly more accurate in measuring the locations because the Muslims used larger instruments.
Muslim astronomers saw the cloudy regions of the sky which we now know are.galaxies, but did not know what they were.
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stars and galaxies
stars forming in the Large Magellanic Cloud
STAR TABLES AND STAR CATALOGS
Star position charts of India reached Baghdad in the 8th century.
In the 9th century the star position tables in Ptolemy’s Almagest were translated into Arabic.
Al-Tusi, Zij-i Ilkhani, Qāḍī Zāda al-Rūmī (1364 i– 1436), Ulugh Beg, al-Kāshī, Qāḍī Zāda and others created star catalogs, often containing approximately 1000 stars.
Shortly after 1424, Ulugh Beg’s (1394 – 1449) catalog had slightly less than the number of stars in Ptolemy’s 2nd century catalog, but was slightly more accurate in measuring the locations because the Muslims used larger instruments.
The plotting of stars onto a sphere is called orthographic projection and was first done by
Al-Battani placed the skeleton of Hipparchus over the celestial sphere of Hipparchus, thereby making the plotting more accurate.
DISTANCE TO STARS
Ptolemy and all Muslim astronomers thought all stars were the same distance from the Earth, and not much further than Saturn.
Al-Biruni thought that all stars were the same distance from the Earth, and located on the surface of a hollow sphere.
Greek philosophers of the 5th century BC correctly thought the Milky Way was composed of stars that appeared to be small because they were further away than other stars.
Avempace (Ibn Bājjah) in 12th century Muslim Spain took a step backwards in incorrectly thinking the Milky Way was the same distance away as other stars but refraction in the Earth’s atmosphere caused the stars to appear to be small and close together.
In 964 AD the Persian astronomer abd al-Rahman al Sufi (903 – 986) was the first astronomer to write about what he called the “little cloud” and the “sheep of the southern Arabs” which we now know are the Andromeda galaxy and a galaxy known as the Large Magellanic Cloud. (The Large Magellanic Cloud cannot be seen in northern latitudes, but was known in ancient times to the people of southeast Asia.) He did not know what they were, how enormous they were, or that they were much further away than the stars we see in the sky.
Image by ESA/Hubble, via Wikimedia Commons.
image credit https://en.wikipedia.org/wiki/File:Starsinthesky.jpg