A Brief History of Astronomy NOTES GEO MEANS EARTH HELIOS MEANS SUN CENTRIC MEANS CENTER There have been 2 main thoughts about how the solar system and universe are set up: Geocentric System: Definition: earth centered model of the universe . Geocentric System: The Greeks: • 4th century BC - Plato and Aristotle wrote about it. Geocentric System: Ptolemy: ’Improved’ the model…to explain zig zag of objects in night sky. Put planets/stars going in circles while orbitting. Heliocentric System: Definition: sun centered model of the solar system Heliocentric System: Copernicus: introduced his idea in 1543 - the same year he died Why do you suppose most people did not believe Copernicus’ idea? FINALLY!! Evidence that supports the heliocentric model is discovered by… …a scientist named GALILEO. 1600’s Italian Astronomer 1st to use a telescope What is the evidence that was discovered using the telescope? 1. There were 4 moons orbiting around Jupiter (not Earth) 2. Venus went through phases like our moon. Who else helped? Brahe and Kepler • Mathematicians who made observations on the shape of the planet’s orbits over a 20 year period. • Brahe’s observations and Kepler’s analysis revealed that the orbits of the planets WERE NOT PERFECT CIRCLES, but ELLIPSES.