1. Greeks Discovered the planets Planet is the greek word meaning wanderers Called wanerers because they sometimes moved in the opposite direction from the rest of the visible stars in the sky

2. Geocentric - Earth is at the center of the solar system all planets, stars and our sun revolves around the Earth

3. Ptolemy’s model Greek astronomer Planets move on small circles along their orbit animation

4. Heliocentric Sun at the center of the solar system Copernicus 1473-1543 Worked out the arangement of the known planets and how they moved around the sun (just a way to know where a planet is located at any given time) Animation

5. Galileo 1564-1642 Used telescope to see moons revolving around Jupiter Why was this important? Also noticed that full phase of Venus is much smaller than cresent phase of Venus Why was this important? Contradicts previous view that everything in the solar system revolves around the Earth.

6. Venus is further from the Earth at full phase. Therefore, it is smaller in size. When Venus is in cresent phase it is close to Earth. Larger.

7. Venus Phases from Earth

9. comparison between geocentric and heliocentric models comparison between geocentric and heliocentric models

10. Tycho Brahe 1546-1601 Over 20 years of detailed observations recording the location of the planets

11. Kepler 1571-1630 Found that the orbit of each planet is an elipse Ellipse - Oval shaped, 2-foci

12. Ellipse vs. Circular Orbit