## KEPLER

Here we are to visit Dr. Pepper, oops Mr. Kepler. "Hello Kepler, can I ask you some questions about your ideas of planetary motion?

"Of course you can."

"Well what is your philosophy of the motion of the planets, as well as the positioning of Earth?"

"Well those are some far out questions. Well you see I was looking over my late teachers work (Tycho Brahe). I noticed a certain relationship between a planet's rotation and the radius from the center of the universe to the planet. I found out that the radius cubed was directly proportional to the period squared. When I calculated a constant value for this, I found that the values for each planetary system was pretty close for each moon. There was about a 5% discrepancy for these values. I then looked back at my values and found that if the orbits of the planets were ellipses, then the values worked out quite well. I then followed this concept up and found that the planets do orbit in ovals, or ellipses, with the Sun at one of the foci of the ellipse. After experimenting with some beer keg barrels I found that if you joined a line from the sun to a planet, it would sweep out equal areas in equal times. Thus, the planet sometimes moves faster, and sometimes closer, depending on your proximity to the sun."

"A very interesting concept Kepler. I would then assume that you believe the universe is heliocentric - the sun at the center"

"Yes I do, and you have a very nice hat"

"Thank you for your time, and yes I do have a nice hat."

Kepler's ideas were revolutionary. He had developed three laws for the planets which are as follows:

1. The planets travel in an elliptical or oval shape

2. The area swept out by a line joining the sun and a planet was equal in equal time intervals

3. The average radius of an object to its center cubed is directly proportional to its period of rotation squared. Kepler changed the way we looked at heavenly motion because he showed that motion in the heavens was not circular like Aristotle had said. It was elliptical, and the sun was at the center of the universe.

Newton