<P> In 499 CE, the Indian astronomer Aryabhata wrote that the spherical earth rotates about its axis daily, and that the apparent movement of the stars is a relative motion caused by the rotation of the Earth . He provided the following analogy: "Just as a man in a boat going in one direction sees the stationary things on the bank as moving in the opposite direction, in the same way to a man at Lanka the fixed stars appear to be going westward ." </P> <P> In the 10th century, some Muslim astronomers accepted that the Earth rotates around its axis . According to al - Biruni, Abu Sa'id al - Sijzi (d. circa 1020) invented an astrolabe called al - zūraqī based on the idea believed by some of his contemporaries "that the motion we see is due to the Earth's movement and not to that of the sky ." The prevalence of this view is further confirmed by a reference 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 ." Treatises were written to discuss its possibility, either as refutations or expressing doubts about Ptolemy's arguments against it . At the Maragha and Samarkand observatories, the Earth's rotation was discussed by Tusi (b . 1201) and Qushji (b . 1403); the arguments and evidence they used resemble those used by Copernicus . </P> <P> In medieval Europe, Thomas Aquinas accepted Aristotle's view and so, reluctantly, did John Buridan and Nicole Oresme in the fourteenth century . Not until Nicolaus Copernicus in 1543 adopted a heliocentric world system did the contemporary understanding of earth's rotation begin to be established . Copernicus pointed out that if the movement of the earth is violent, then the movement of the stars must be very much more so . He acknowledged the contribution of the Pythagoreans and pointed to examples of relative motion . For Copernicus this was the first step in establishing the simpler pattern of planets circling a central sun . </P> <P> Tycho Brahe, who produced accurate observations on which Kepler based his laws, used Copernicus's work as the basis of a system assuming a stationary earth . In 1600, William Gilbert strongly supported the earth's rotation in his treatise on the earth's magnetism and thereby influenced many of his contemporaries . Those like Gilbert who did not openly support or reject the motion of the earth about the sun are often called "semi-Copernicans". A century after Copernicus, Riccioli disputed the model of a rotating earth due to the lack of then - observable eastward deflections in falling bodies; such deflections would later be called the Coriolis effect . However, the contributions of Kepler, Galileo and Newton gathered support for the theory of the rotation of the Earth . </P>

What is the axis of rotation of the earth