# Labs from Chicago, Fall 1993 : Kepler's First Law.

Dr. Jim Sweitzer
Labs written for the CARA Space Explorers, Fall 1993

This is meant to be handed out to the students.

## Introduction

The satellites we will be studying in class are artificial satellites of the Earth. There are many natural satellites out in the Solar System. In fact we are riding on a big one orbiting the Sun. This short activity sheet will introduce you to Kepler's first law of planetary motion. This scientific law relates the period of a planet's orbit to the average distance the planet orbits from the Sun.

Kepler studied to be a Lutheran minister, but he was first employed as a high school math teacher and astronomer. He lived and worked in southern Germany and Prague. He lived between 1571 and 1630. He was one of the first astronomers to be totally converted to the ideas of Copernicus. He discovered three laws of planetary motion. Today you will just learn about the first.

Fill in the blanks in the following table. The ones that I have put in are known quantities. Do what is asked for in the column three and five for the planets. The unknown object, 1993 SB, was just discovered last month. Only fill in column three for it now. What do you notice about these two columns when you are done?

Planet  Average Distance  D^3   Orbital Period    P^2
from Sun in               in years
au* = D                   = P
Mercury      .39                     0.24
Venus        .72                     0.62
Earth       1.0	                     1.0
Mars        1.5	                     1.9
Jupiter     5.2                     12
Saturn      9.5	                    29
1993 SB	   33
(*) 1 AU is an Astronomical Unit, the distance between the Earth and the Sun.

Now find the orbital period for the newly discovered object, 1993 SB.

Kepler's first law can be written as an equation. For the units we have used above, it is:

D = P.