VOCABULARY

3. the object's orbital motion around another object
4. a huge collection of dust, gas, and billions of stars and their solar systems, all held together by gravity
6. any theory of the structure of the solar system (or the universe) in which Earth is assumed to be at the centre of it all
9. time based on the meridian through a particular place as contrasted with that of a time zone
12. group of stars that appears to form a pattern or picture
14. cosmic snowballs of frozen gases, dust, rock that orbit the sun
15. vertical elevation of an object above a surface
17. objects in space such as the sun, moon, planets, and stars
18. everything that exists, especially all physical matter, including all the stars, planets, galaxies, etc
19. very long-period waves that move through the ocean in response to the forces exerted by the moon and sun
20. a center of activity, attraction, or attention

1. astronomical model in which the Earth and planets revolve around the sun at the center of the universe
2. the action of rotating around an axis or center
5. absolute measure of radiated electromagnetic power light, the radiant power emitted by a light-emitting object over time
7. a closed plane curve generated by a point moving in such a way that the sums of its distances from two fixed points is a constant
8. the sun together with the group of celestial bodies that are held by its attraction and revolve around it
10. a freely swinging pendulum that consists of a heavy weight hung by a long wire
11. small rocky body that orbits the sun
13. a small body of matter from outer space that enters the Earth's atmosphere
16. a complete or partial hiding of the sun caused by the moon's passing between the sun and the Earth