Seleucus of Seleucia

Seleucus (or Seleukos) of Seleucia (born "c." 190 BC, "fl." 150s BC) was a Babylonian astronomer from the Seleucia region of Mesopotamia who supported the heliocentric theory of planetary motion. Seleucus is known from the writings of Plutarch, Strabo and Aetius. He was a Chaldean born in Seleucia on the Tigris in Babylonia. [Otto E. Neugebauer (1945). "The History of Ancient Astronomy Problems and Methods", "Journal of Near Eastern Studies" 4 (1), p. 1-38.quote|"the Chaldaean Seleucus from Seleucia"] [George Sarton (1955). "Chaldaean Astronomy of the Last Three Centuries B. C.", "Journal of the American Oriental Society" 75 (3), p. 166-173 [169] .quote|"the heliocentrical astronomy invented by Aristarchos of Samos and still defended a century later by Seleucos the Babylonian"] [William P. D. Wightman (1951, 1953), "The Growth of Scientific Ideas", Yale University Press p.38, where Wightman calls him Seleukos the Chaldean.]

Teaching around 150 BC, he agreed with the heliocentric theory of Aristarchus of Samos, which stated that the Earth rotated around its own axis which in turn revolved around the Sun. [We do not know other names of ancient astronomers or scientists who supported the heliocentric system: Hipparchus and later Ptolemy contributed to the success of the geocentric system; however, in the writings of Plutarch and Sextus Empiricus we read of "the followers of Aristarchus", thus it is probable that other people we do not know of adhered to the heliocentric view.] According to Plutarch, Seleucus was the first to prove the heliocentric system through reasoning, but it is not known what arguments he used.

Tides

According to Lucio Russo, Seleucus' arguments for a heliocentric theory were probably related to the phenomenon of tides. [Lucio Russo, "Flussi e riflussi", Feltrinelli, Milano, 2003, ISBN 88-07-10349-4.] 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. [Bartel Leendert van der Waerden (1987). "The Heliocentric System in Greek, Persian and Hindu Astronomy", "Annals of the New York Academy of Sciences" 500 (1), 525–545 [527] .]

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, like what 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. [Bartel Leendert van der Waerden (1987). "The Heliocentric System in Greek, Persian and Hindu Astronomy", "Annals of the New York Academy of Sciences" 500 (1), 525–545 [527-529] .] .

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 they do not leave the Sun for more than a certain angle.

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