Persian astronomer Abd al-Rahman al-Sufi (903–986), known as Azophi to Westerners, made the first known observation (opens in new tab) of a group of stars outside of the Milky Way, the Andromeda galaxy. (Image credit: Bartolomeu Velho) Abd al-Rahman al-Sufi The Ptolemaic geocentric model of the universe, devised by the Greek scientist Claudius Ptolemy, had everything revolving around Earth. However, his model, which was incorrect, later fell out of use as the heliocentric view of the solar system came into being.įew details about Ptolemy's life survived to the present day. Ptolemy's writings stood as authoritative for more than 1,200 years. Ptolemy also catalogued 48 constellations, the names of which are still in use at present. This Ptolemaic system presented tables of information allowing convenient predictions of planetary locations. It expanded Hipparchus’ geometric model of celestial motions, utilizing epicycles and eccentric circles in a geocentric theory which placed the Earth at the center of the solar system. In the 2nd century, Ptolemy published the Almagest (opens in new tab), a comprehensive treatise on the movements of the stars and planets. According to NASA (opens in new tab), "Ptolemy represents the epitome of knowledge of Grecian astronomy." As a mathematician, geographer and astronomer, he authored several scientific texts which had considerable impact on Western intellectual thought.
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