- Ptolemy placed the Earth at the center of the universe, with the Moon, Mercury, Venus, the Sun, Mars, Jupiter, and Saturn circling the Earth. This geocentric model held sway for 1400 years. - Copernicus proposed that the Sun, not the Earth, was the center of the Solar System in his book On the Revolutions of the Heavenly Bodies. This heliocentric model made Copernicus the "father of modern astronomy." - Kepler formulated his Three Laws of Planetary Motion using Brahe's precise observations. The first law states that the orbits of the planets are ellipses with the Sun at one focus.

1. History of Astronomy

26. Some Properties of Ellipses

48. What Really Happened with the Apple?

50. SUMMARY Earth is the center of motion Earth is does not move Earth IS flat Planets move in circular orbits Stars are immutable Galileo Galilean satellites Phases of Venus Universal Law of Gravitation Newton Laws of Motion Einstein Theory of Relativity Kepler Laws of Planetary Motion Brahe Supernova