There was a lot of controversy in the past...

(AD 90 - AD 168)
image credit: http://en.wikipedia.org/wiki/File:Ptolemaeus.jpg image credit: http://en.wikipedia.org

Ptolemy was one of the most influental Greek astronomers and mathematicians of his time. Ptolemy derived a geocentric model from astronomical observations in his hometown Alexandria in Egypt.

The stationary Earth is placed in the center of the Universe. Moon, Mercury, Venus, Sun, Mars, Jupiter, and Saturn are stacked above the Earth and orbit about it whereas the stars are fixed in a sphere enclosing the earth.)

Since Ptolemy used the most accurate observations, planetary positions could be calculated with reasonable accuracy. His geocentric model prevailed for about 1400 years and was universaly accepted until Copernicus proposed a heliocentric theory in 1543 (the era of scientific revolution).

Here is an animation showing planetary motions given a geocentric model.

In Contrast to Ptolemy, Copernicus developed the heliocentric model placing the Sun in the center of the Solar system. Thus, the planets orbit the Sun on eccentric cycles.

Copernicus' vision of the Universe also implies that any motion which appears in the firmament arises from the motion of the Earth. The Earth itself is performing one complete rotation in one day while the stars in the firmament stay fixed.

Since the predictions of this revolutionary model were not significantly better than those of the Ptolemaic theory it was only slowly accepted.

Here you can view an animation given a heliocentric model.

Last modified: 23 Aug 2012, 09:23 CET