Seleucus (or Seleukos) of Seleucia (born c. 190 BC, fl. 150s BC) was a Hellenistic astronomer and philosopher from the Seleucia region of Mesopotamia who supported the heliocentric theory of planetary motion.^[1][2][3] Seleucus is known from the writings of Plutarch, Strabo and Aetius. He was a Chaldean born in Seleucia on the Tigris in Babylonia.^[4][5][6]

Teaching around 150 BC, he is known to have been the only 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.^[7][8] According to Plutarch, Seleucus was the first to prove the heliocentric system through reasoning, but it is not known what arguments he used.

[edit] Tides

According to Lucio Russo, Seleucus' arguments for a heliocentric theory were probably related to the phenomenon of tides.^[9] Seleucus correctly theorized that tides were caused by the Moon, although he believed that the interaction was mediated by the pneuma. He noted that the tides varied in time and strength in different parts of the world.

According to Strabo (1.1.9), Seleucus was the first to state that the tides are due to the attraction of the Moon, and that the height of the tides depends on the Moon's position relative to the Sun.^[10]

[edit] Computational model

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, 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.^[11].

Since the time of Heraclides of Pontus or Heraclides Ponticus (387 BC-312 BC), the inferior planets Mercury and Venus are named at times solar planets, as their positions diverge from the Sun by only a small angle.

[edit] References

[edit] See also

• Babylonian astronomy