| A | B |
|---|
| wanderer | the word "planet" means... |
| round | greek astronomers think the earth is... |
| earth | heavenly body Ptolemy believed was center of universe... |
| sun | Copernicus believed this was center of solar system... |
| Kepler | German astronomer who formulated the three laws of planetary motion... |
| astronomical unit | masure based upon the average distance between earth and sun... |
| Sir Isaac Newton | English scientist who discovered gravity... |
| foci | two central points of an ellipse |
| ellipse | planets travel around the sun in an orbit shaped like an... |
