Across
- 5. first person to use a telescope to observe the sky. Found that four moons orbit Jupiter, proving that not all objects in space orbit the earth.
- 6. a oval that is centered on 2 points instead on one. The shape our planets orbit our sun.
- 8. The apparent backward movement of a planet
- 9. (AU) Distance in space is often measured in AU. 1 AU = to 1.496 x 108 km. 1 AU is the average distance from earth to the sun.
- 10. when the earth are closed to the sun
- 12. one of two fixed points, used to define an ellipse
Down
- 1. The shape of a planet's elliptical orbit is defined by this. It is the ratio of the distance between the foci to the length of of the major axis
- 2. He found that the planets orbit the sun not in a circus but in a ellipse shape. Also found that planets move faster when they are closer to the sun
- 3. Objects that range from 1 kilometer to hundreds of kilometers in diameter. Made from colliding particles in the early solar system. These eventually form planets
- 4. When the earth are furthest from the sun
- 7. 1543, suggested that the sun was the center of the solar system and that all the planets orbited the sun
- 11. Developed understanding of gravity as an attractive force between two objects. He made the law of universal gravitation. This explained why planets move according to Kepler's laws.