1. History of Astronomy The guys with their eyes on the skies

2. Greeks: Aristotle

3. Claudius Ptolemy 140 AD Believed in the geocentric model (earth centered) orbits were perfect circles because it looked like Mars was traveling backward sometimes he added circles to the orbits (epicycles) E M M

4. epicycles

5. Nicolaus Copernicus Early 1500's Developed heliocentric model (sun-centered) With geometry: figured out distance to Sun Still thought orbits were perfect circles

6. Galilei Galileo Early 1600's Using the telescope he proved the heliocentric model with the following discoveries: 4 moons orbiting Jupiter phases of Venus did experiments with falling objects-Inertia

7. sun Johannes Kepler 1600's proved that orbits were NOT perfect circles: they are ellipses

8. Sir Isaac Newton 1665 explained why the planets stay moving around the sun: inertia and gravity 1st law: inertia-a body will continue in a straight line unless acted on by a force. Gravity keeps them moving planets in orbit around Sun

10. Edwin Hubble 1920’s Heliocentric Showed that there were galaxies out there besides ours Hubble’s Law: the farther something was from Earth, the faster away it was moving. Universe is still expanding!!.