page_title: Astronomy in the medieval Islamic world
section_title: Earth rotation
hierarchical_section_title: Astronomy in the medieval Islamic world / Golden Age / Earth rotation
caption_attribution_description: العربية: مخطوطة بِيد أبي الريحان البيروني (973-1048م) تتناول أطوار أو مراحل القمر المُختلفة، من كتاب التفهيم (المخطوط بِالفارسيَّة). تعريب التعليق: English: Illustration of different phases of the moon, from manuscript of the Kitab al-Tafhim by Al-Biruni (973-1048). فارسی: جایگاه‌های مختلف ماه در کتاب التفهیم اثر ابوریحان بیرونی.
context_page_description: Islamic astronomy comprises the astronomical developments made in the Islamic world, particularly during the Islamic Golden Age, and mostly written in the Arabic language. These developments mostly took place in the Middle East, Central Asia, Al-Andalus, and North Africa, and later in the Far East and India. It closely parallels the genesis of other Islamic sciences in its assimilation of foreign material and the amalgamation of the disparate elements of that material to create a science with Islamic characteristics. These included Greek, Sassanid, and Indian works in particular, which were translated and built upon.
  Islamic astronomy played a significant role in the revival of Byzantine and European astronomy following the loss of knowledge during the early medieval period, notably with the production of Latin translations of Arabic works during the 12th century.
  Islamic astronomy also had an influence on Chinese astronomy and Malian astronomy.
  A significant number of stars in the sky, such as Aldebaran, Altair and Deneb, and astronomical terms such as alidade, azimuth, and nadir, are still referred to by their Arabic names.
context_section_description: Abu Rayhan Biruni (b. 973) discussed the possibility of whether the Earth rotated about its own axis and around the Sun, but in his Masudic Canon, he set forth the principles that the Earth is at the center of the universe and that it has no motion of its own. He was aware that if the Earth rotated on its axis, this would be consistent with his astronomical parameters, but he considered this a problem of natural philosophy rather than mathematics. 
  His contemporary, Abu Sa'id al-Sijzi, accepted that the Earth rotates around its axis. Al-Biruni described an astrolabe invented by Sijzi based on the idea that the earth rotates:
  I have seen the astrolabe called Zuraqi invented by Abu Sa'id Sijzi. I liked it very much and praised him a great deal, as it is based on the idea entertained by some to the effect that the motion we see is due to the Earth's movement and not to that of the sky. By my life, it is a problem difficult of solution and refutation. [...] For it is the same whether you take it that the Earth is in motion or the sky. For, in both cases, it does not affect the Astronomical Science. It is just for the physicist to see if it is possible to refute it.
  
  The fact that some people did believe that the earth is moving on its own axis is further confirmed by an Arabic reference work from the 13th century which states:
  According to the geometers [or engineers] (muhandisīn), the earth is in constant circular motion, and what appears to be the motion of the heavens is actually due to the motion of the earth and not the stars.
  At the Maragha and Samarkand observatories, the Earth's rotation was discussed by al-Kātibī (d. 1277), Tusi (b. 1201) and Qushji (b. 1403). The arguments and evidence used by Tusi and Qushji resemble those used by Copernicus to support the Earth's motion. However, it remains a fact that the Maragha school never made the big leap to heliocentrism.
caption: An illustration from al-Biruni's astronomical works, explains the different phases of the moon, with respect to the position of the sun.
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