<P> Since Plutarch mentions the "followers of Aristarchus" in passing, it is likely that there were other astronomers in the Classical period who also espoused Heliocentrism, but whose work was lost . The only other astronomer from antiquity known by name who is known to have supported Aristarchus' heliocentric model was Seleucus of Seleucia (b . 190 BC), a Hellenistic astronomer who flourished a century after Aristarchus in the Seleucid empire . Seleucus adopted the heliocentric system of Aristarchus and is said to have proved the heliocentric theory . According to Bartel Leendert van der Waerden, Seleucus may have proved the heliocentric theory by determining the constants of a geometric model for the heliocentric theory and by developing methods to compute planetary positions using this model . He may have used early trigonometric methods that were available in his time, as he was a contemporary of Hipparchus . A fragment of a work by Seleucus has survived in Arabic translation, which was referred to by Rhazes (b . 865). </P> <P> Alternatively, his explanation may have involved the phenomenon of tides, which he supposedly theorized to be caused by the attraction to the Moon and by the revolution of the Earth around the Earth - Moon' center of mass' . </P> <P> There were occasional speculations about heliocentrism in Europe before Copernicus . In Roman Carthage, the pagan Martianus Capella (5th century A.D.) expressed the opinion that the planets Venus and Mercury did not go about the Earth but instead circled the Sun . Capella's model was discussed in the Early Middle Ages by various anonymous 9th - century commentators and Copernicus mentions him as an influence on his own work . </P> <P> The Ptolemaic system was also received in Indian astronomy . Aryabhata (476--550), in his magnum opus Aryabhatiya (499), propounded a planetary model in which the Earth was taken to be spinning on its axis and the periods of the planets were given with respect to the Sun . He accurately calculated many astronomical constants, such as the periods of the planets, times of the solar and lunar eclipses, and the instantaneous motion of the Moon . Early followers of Aryabhata's model included Varahamihira, Brahmagupta, and Bhaskara II . </P>

What does it mean to say that the earth revolves around the sun once each year