Early History of Astronomy

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ACROSS
6. The kind of motion that occurs when planets drift backward (compared to their usual direction) against the background stars.
7. A theory of the Universe that has the Sun at its center.
10. Greatest _________. When an inferior planet appears as far as possible from from the Sun in the sky.
11. When a superior planet appears to line up with Sun in the sky.
13. The last name of the Danish nobleman who used giant instruments to make observations of the planetís motions with unprecedented accuracy.
14. In the Ptolemaic model of the Universe, planets moved uniformly around small circles, centered on these larger circles.
15. When a superior planet appears to line up with Sun in the sky.
16. In the Ptolemaic model of the Universe, planets moved uniformly around these small circles, which were centered on larger circles.
17. When looking south, a planet may be seen to the right, or _____ of the Sun.
DOWN
1. This 19th century French physicist used a pendulum to prove that the Earth moves.
2. This Greek philosopher (around 350 B.C.) thought that the Earth was at the center of the universe.
3. The first name of the Danish nobleman who used giant instruments to make observations of the planetís motions with unprecedented accuracy.
4. A theory of the Universe that has the Earth at its center.
5. This man calculated the correct size of the Earth in about 250 B.C.
8. When looking south, a planet may be seen to the left, or _____ of the Sun.
9. This 16th century Polish astronomer became famous for his theory that the Sun was at the center of the universe and that the Earth moved.
12. This 2nd century astronomer used an Earth-centered model with circles-on-circles (epicycles) to explain the motion of the planets.

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