Suggested much earlier, the heliocentric model is attributed to NicholasĬopernicus who wrote the first 'modern' description in his book, De To fit almost any situation within the accuracy of observations of his These adjustments, always involving perfect circles, could be adjusted

Motion and the fact that planets vary in brightness, Ptolemy introduced Planets moving in perfect circles around the Earth, could not account for These motions can be demonstrated in any planetarium program (e.g. Mercury and Venus, never wander very far from the Sun, and so reach a maximumĪngular distance, called greatest elongation. Stop, reverse direction ( retrograde motion), Where they often become faintest, and they appear opposite the Sun ( opposition ), They align with the Sun ( conjunctions ), Observations of the sky over many years show that planets obey certain 150 BC) proposed a system of circles to explain the odd motions of the planets as seen from Earth. Having to do with the heavens had to be perfect, hence circular. Handed down from Aristotle (384-322 BC) was the notion that all motions

The Sun and planets going around it (attached to heavenly spheres). Or geocentric, system, it placed the immovable Earth at the center, with 'obvious' model that originated in prehistory. 100 AD) in his 13-book work, the Almagest, although it is an System, because it was written down by Claudius Ptolemy The Ptolemaic System The ancient modelįor the solar system is called the Ptolemaic

Retrograde motion definition