Question

Can someone explain Kepler's law to me? Thanks!

Answer 1

1. The orbit of every planet is an ellipse with the Sun at one of the two foci.
There is an ellipse, or a circle, that every planet orbits the sun with. In this ellipse, there are two foci, one if it a circle, and one of the foci will always be the sun.
2. A line joining a planet and the Sun sweeps out equal areas during equal intervals of time.
Think of this like there is a ball attached to a pole with a rope; every time the ball goes around, it covers the same area as it did before, even if swings out more on one side. This is because as a planet goes out at wider distances, like Pluto, it comes around the other side of the sun, or focus, and travels faster here and for a shorter distance. Because of this, the planets orbit with an equal area covered.
3. The square of the orbital period of a planet is directly proportional to the cube of the semi-major axis of its orbit.
This law compares the orbital periods. If planet A is 4 times further away from the sun than planet B is, planet A has to traverse 4 times the distance that planet B does. Furthermore, If planet A is traveling slower at 1/2 the speed of planet B, than it planet A takes 8 time longer: 4*2=8\[6^{2}\]. Now to apply it to the law:
\[4^{3}=8^{2}\] This is directly proportional to the cube of the orbit and the orbital period squared.