Geocentric Theory and Heliocentric theory

Geocentric Theory Who? Greek philosophers and astronomers What? The earth is stationary and at the center of the universe Planets orbit on the surface of hollow, transparent spheres Stars were attached to the outermost sphere Who? Greek philosophers and astronomers Hipparchus – (190-120 BC) Greek who developed a mathematical geocentric model and cataloged 850 stars Ptolemy – (AD 85-165) Egyptian who attempted to improve the geocentric theory

Geocentric theory Problems: 1. Planets sometimes appear to be large, bright, and close; other times, smaller, dimmer, and farther away. 2. Could not explain why certain planets were observed to slow down, stop, and then back up before resuming their forward motion. 3. Inaccurate – there were discrepancies between observations and the model

Heliocentric theory What? The sun is at the center of the solar system Who? Copernicus – stationary sun and moving earth; wrote The Revolutions; Copernican theory = heliocentric theory Tycho – very accurate astronomical observer Kepler – laws of planetary motion; modified and improved heliocentric theory; orbits are elliptical; wrote New Astronomy Galileo – first to see Saturn’s rings; first to see Jupiter’s moons; tried by the Catholic Inquisition for promoting heliocentric theory Newton – law of gravity; according to tradition, he was inspired by an apple falling from a tree