Geocentric Model

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The Ptolemaic system

Synonym: Ptolemaic World-View

History

Until the Copernican Revolution, the commonly held world-view was that the "sublunar sphere" of the earth is the centre of the universe around which the sun, moon, planets and the fixed stars revolve. The basis for this view is the subjective human perception of the cosmos which is unavoidably geocentric in nature. This idea lay at the heart of the system devised by the ancient Babylonians and was transmitted to medieval Europe via the books of the Hellenistic astrologer and astronomer Ptolemy. It had a lasting influence on cosmological beliefs until Copernicus published his ideas on the heliocentric model. Judaism, Christianity and Islam all lent support to the geocentric world-view because of affirmed scriptural passages that seemingly placed the earth in the center of the cosmos.

The Ptolemaic order of spheres from Earth outward is:

  1. Moon A35_150.gif (lunar sphere)
  2. Mercury A34_146.gif
  3. Venus A25_087.gif
  4. Sun A39_209.gif
  5. Mars A33_140.gif
  6. Jupiter A29_112.gif
  7. Saturn A26_087.gif (the farthest planet)
  8. Fixed stars
  9. Primum Mobile (First Moved)

Modern astrology is still based on a geocentric world-view. The reasoning has nothing to do with remaining loyal to tradition or ignoring scientific discoveries but rather because human experience of the cosmos is literally geocentric: humans observe celestial events from the earth. The individual's position is at the centre of a horoscope with the planets rotating around this centre.

See also

The basic elements of Ptolemaic astronomy[1]

Weblinks

Bibliography

  • Giorgio de Santillana, 1955, The Crime of Galileo, University of Chicago Press; pp. 40-47, 93

Notes and References

  1. Showing a planet on an epicycle. The Green shaded area is the celestial sphere which the planet occupies