Friday, April 22, 2011

Seleucus of Seleucia

Seleucus (or Seleukos) of Seleucia (born c. 190 BC, fl. 150s BC) was a hellenized Babylonian astronomer and philosopher who stood in the tradition of Hellenistic astronomy. Coming from Seleucia on the Tigris, the capital of the Seleucid empire, or, alternatively, Seleukia on the Red Sea, he is best known as a proponent of heliocentrism and for his theory of the origin of tides.
According to Lucio Russo, Seleucus' arguments for a heliocentric theory were probably related to the phenomenon of tides. 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 Lucio Russo, Seleucus ascribed tides both to the Moon and to a whirling motion of the Earth, which could be interpreted as the motion of the Earth around the Earth-Moon center of mass. This latter motion is in fact the actual cause of tides on the side of the Earth opposite to the one facing the Moon.

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