| A | B |
|---|
| heliocentric | sun-centered model |
| Venus phases | Galileo observed;supports heliocentric |
| Copernicus | man known for heliocentric theory |
| geocentric | earth-centered model |
| gravity and inertia | forces which keep planets in orbit |
| inertia | tendency of objects to continue in a straight line |
| Kepler | known for elliptical orbit discovery |
| Brahe | known for planet position theory |
| nuclear fusion | sun's energy source |
| Romans | names/symbols of early planets |
