March 7, 2007

Alg: no hw

Es: signed test corrections due 3/ 9

Eng: Study for oedipus test

Global: study for Africa test 3/9

Motion in the Solar System

I. Motion in the Solar System
A. Johannes Kepler developed 3 laws of planetary motion we need to
understand:
1. 1st Law of Planetary Motion - all planets have elliptical orbits.
- at aphelion, a planet is its farthest from the sun
- at perihelion, a planet is its closest to the sun
2. 2nd Law of Planetary Motion - the equal area law. An
imaginary line connecting the planets to the sun sweeps
over equal areas of an ellipse in equal amounts of time.

A diagram showing a planet on its elliptical orbit around the Sun. The shaded areas are of equal size, and were swept out in equal time, i.e. it took the same amount of time for the planet to move from A to B and from C to D.
(see diagram below)

II. Solar System Models
A. Geocentric model - earth is the center of the universe. Proposed
by Ptolemy in 140 AD.

B. Heliocentric model - sun is center of solar system. Proposed by
Copernicus in the 1600’s.