Seleucus is known to have been a follower of the heliocentric theory of Aristarchus of Samos, which stated that the Earth rotated around its own axis which in turn revolved around the Sun. According to Plutarch, Seleucus was the first to demonstrate the heliocentric system through reasoning, but it is not known what arguments he used. According to Bartel Leendert van der Waerden, Seleucus may have constructed his heliocentric theory by determining the constants of a geometric model and by developing methods to compute planetary positions using this model, as Nicolaus Copernicus later did in the 16th century. He may have used trigonometric methods that were available in his time, as he was a contemporary of Hipparchus.