GEOCENTRIC THEORY AND HELIOCENTRIC THEORY GEOCENTRIC THEORY What

GEOCENTRIC THEORY AND HELIOCENTRIC THEORY

GEOCENTRIC THEORY • 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