1. Kepler and Planetary Motion
NC Essential Standards for Earth
And Environmental Science
Created Fall 2012

2. The Center of the Universe is….
Ptolemy vs. Copernicus
Ptolemy
Copernicus
Geocentric Theory:
The Earth is the center of the Universe.
Heliocentric Theory:
The Sun is the center of the Universe.

3. Johannes Kepler
Kepler’s greatest contribution to astronomy was his three laws of planetary motion.
Kepler's three laws of planetary motion can be described as follows:
First Law: The Law of Ellipses
Second Law: The Law of Equal Areas
Third Law: The Law of Harmonies

4. Kepler’s 1st Law: The Law of Ellipses
The path of the planets about the sun is elliptical in shape, with the center of the sun being located at one focus.
An ellipse has two foci.
The sun is at one of the foci.
At certain times of the year, the planet is closer to the sun.
For the Earth, the Earth is closest to the sun on January 4th and furthest away from the sun on July 4th.

5. Eccentricity of the elliptical orbit
Eccentricity means “out of roundness” – how far from a circular orbit is it?

6. Kepler’s 2nd Law: The Law of Equal Areas
An imaginary line drawn from the center of the sun to the center of the planet will sweep out equal areas in equal intervals of time.
When the planet is closest the sun, the planet is moving fastest.
When the planet is farthest from the sun, it is moving slowest.

7. Kepler’s 3rd Law: The Law of Periods or Harmonic Law
This law relates the time required by a planet to make a complete trip around the Sun to its mean distance from the Sun. This law can be simply stated as:
The ratio of the squares of the periods of any two planets is equal to the ratio of the cubes of their average distances from the sun.
p2 ∝ a3 p = the orbital period
a = the semi-major axis of the orbit

8. So what good is Law 3?
If you know a planet’s average distance to the sun, you can calculate the revolution of the planet around the sun.
This provided mathematical proof that planets further from the sun take longer to go around the sun.

9. Significance of Kepler’s Laws
The laws of planetary motion proved very significant for space travel, providing necessary answers to a number of questions. It told astronomers how long it would take to enter into orbit around another planet and how to put a satellite into synchronous orbit around the Earth.
Read more: Laws of Planetary Motion | eHow.com