1. Cool Dudes of Astronomy! a.k.a A brief history of astronomy

2. Ancient Greeks Observed patterns in the stars that didn’t move or change- the stars moved, but stayed in the same position relative to each other. Observed 5 points of light that seemed to wander among the stars – planets (wandering star) Mercury Venus Mars Jupiter Saturn

3. Earth was the center of the universe geocentric Greek for Earth center http://csep10.phys.utk.edu/astr161/lect/retrograde/aristotle.html

4. Ptolemy AD 140 Greek Astronomer Earth is the center of a system of planets The planets move on little circles that move on bigger circles around the earth Curt Suplee, Milestones of Science p.24 http://www.polaris.iastate.edu/EveningStar/Unit2/unit2_sub1.htm

5. This vision of the Ptolemaic universe from a 1660 celestial atlas, shows the position of the Earth surrounded by the celestial circles These ideas lasted for 1400 years! Curt Suplee, Milestones of Science p.24-25

6. Copernicus Believed the sun was at the center of the universe Heliocentric His work was published in1543 – while he was on his deathbed! Sun

7. Galileo ~100 yr after Copernicus Observed 4 moons revolving around Jupiter Observed Venus has phases like our moon

8. Neither of these observations can be explained with Earth at the center, therefore the sun is at the center! Copernicus was correct!! Galileo believed the orbits are circles Galileo cont.

9. Tycho Brahe (TEE koh BRAH uh) 1546-1601 Danish Astronomer – made very careful observations of the planets for almost 20 yr.

10. Johannes Kepler 1600’s Analyzed Brahe’s data Discovered the orbit of each planet is an ellipse.

11. Sir Isaac Newton Inertia and gravity combine to keep the planets in orbit!