Let's start out by looking at the physics behind the orbits of some artificial satellites.
You may notice a pattern here. Can you find a relationship between the radius of an orbit and its period?
We can use Kepler's Third Law everywhere -- even outside our own Solar System -- as long as we are careful. In the past few decades, astronomers have discovered some planets orbiting other stars: to so-called extra-solar planets.
Copyright © Michael Richmond. This work is licensed under a Creative Commons License.