Ibn al-Shatir (1304-1375 AD) was an Arab astronomer and mathematician who made important contributions to the field of astronomy. He is best known for his astronomical tables and for making improvements to the Ptolemaic system, which was the prevailing model of the solar system at the time. He also developed a new method for determining the positions of the planets, which was more accurate than previous methods. He also made a number of other contributions, including the invention of a sundial that could be used to determine the time of prayer.
Ibn al-Shatir's method for determining the positions of the planets was a significant improvement over the Ptolemaic system, which was the prevailing model of the solar system at the time. He made several key modifications to the system that allowed for more accurate predictions of the positions of the planets.
One of his main contributions was the introduction of an epicycle-deferent model, which was a more complex and accurate representation of the motions of the planets than the Ptolemaic model. In this model, each planet moves on a small circle (the epicycle) that is centered on a larger circle (the deferent). The center of the deferent is not the center of the Earth, but is instead offset from the center of the Earth. This offset is known as the "equant point."
Ibn al-Shatir's epicycle-deferent model was able to accurately predict the positions of the planets, including the retrograde motion of the planets, which the Ptolemaic model could not explain.
Another contribution of Ibn al-Shatir was the introduction of a new model for the motion of the Moon, which was more accurate than the Ptolemaic model. This new model was able to predict the Moon's position to within 1 degree of accuracy.
Ibn al-Shatir also made improvements to the Ptolemaic system by using a more accurate value for the length of the year, which allowed for more accurate predictions of the positions of the planets.
In addition to these contributions, Ibn al-Shatir also made other important contributions to the field of astronomy. He designed and built astronomical instruments, such as a sundial that could be used to determine the time of prayer, and he wrote several books on astronomy, including the "Zij al-Ra'id" which was a set of astronomical tables.
Ibn al-Shatir's work had a great impact on the development of Astronomy and it was widely used by astronomers of his time. His methods and models were still used for centuries after his death.
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