KEPLER’S LAWS

First law: Orbits of all the planets are ellipses with the sun at one of the focal points.

Second law: Any planet moves by such a way that radius-vector from the sun to the planet covers in equal time intervals the equal areas.

Third law: T2/a3=const, where T is the period of the planet revolution, a is the length of the bigger axis of the orbit.

The animation here shows the motion of a satellite in a highly elliptical orbit. We can see from this animation that in accordance with Kepler’s first law, the earth is situated at one of the focuses of the orbit and the satellite moves quicker at perigee (the point of the orbit that is nearest to the earth), than in apogee (the point of the orbit that is the most distant from the earth). Such highly elliptical orbits are, in fact, actually used for satellite telecommunication. Unlike the geo-stationary orbit, the satellites on elliptical orbits can "see" the poles of the earth. At apogee, the satellite moves slowly and hangs there for several hours. During these several hours, the satellite provides stable telecommunication, and then its place is taken by another satellite. Thus, several satellites in elliptical orbit are used to provide permanent telecommunication. (See also the explanations on "Iridium" system, which uses 66 low earth orbit satellites).