1. © 2010 Pearson Education, Inc. Chapter 3 The Science of Astronomy

2. © 2010 Pearson Education, Inc. Greeks were the first people known to make models of nature. They tried to explain patterns in nature without resorting to myth or the supernatural. Greek geocentric model (c. 400 B.C.) Why does modern science trace its roots to the Greeks?

3. © 2010 Pearson Education, Inc. How did the Greeks explain planetary motion? Plato: All heavenly bodies move in perfect circles at constant speed. Aristotle: Earth’s position at the center of the universe is a natural consequence of gravity. Aristotle Plato

4. © 2010 Pearson Education, Inc. The most sophisticated geocentric model was that of Ptolemy (A.D. 100-170) — the Ptolemaic model: Ptolemy

5. © 2010 Pearson Education, Inc. In Ptolemy’s model, planets really do go backward.

6. © 2010 Pearson Education, Inc. How did Copernicus, Tycho, and Kepler challenge the Earth-centered model? Copernicus (1473-1543) Proposed a Sun-centered model (published 1543) But... The model was no more accurate than the Ptolemaic model in predicting planetary positions, because it still used perfect circles.

7. © 2010 Pearson Education, Inc. Tycho Brahe (1546-1601) Compiled the most accurate naked eye measurements ever made of Mars. Used the moon’s parallax to determine that a nova and supernova he observed were not in the Earth’s atmosphere, but lay much farther away.