KEPLER’S LAWS
Many motions in the real world are not exactly circular, one of the most important
examples being planetary orbits. Three laws, known as Kepler’s Laws, describe
the motion of planets around the Sun.
The Skinny on Kepler’s Laws
First Law: The orbit of each planet is an ellipse and the sun is at one
focus.
Second Law: An imaginary line from the sun to a moving planet sweeps
out equal areas in equal intervals of time.
Third Law: The ratio of the square of a planet’s period of revolution (the
time for one complete orbit) to the cube of its average distance from the
sun is a constant that is the same for all planets.Kepler’s First Law
Every planet moves in an elliptical orbit, with the sun at one focus. Just as a circle
has a center—that special point inside the circle from which every point on the
circle is the same distance—an ellipse has two foci (plural of focus): A pair of
special points inside the ellipse such that the sum of the distance of every point on
the ellipse to the two foci is always the same.