Why satellites are directly above the equator?

Question

Why satellites are directly above the equator? and all at the same height? is it related to kepler's 3rd law?

Answer 1

As most people have said already only the geosynchronous satellites are directly above the equator and always about 36000 km above the earth. The reason is because this orbit is very convenient for telecoms, weather and TV/radio applications. When a satellite is orbiting at 36000 km above the earth then its orbital period is 24hrs dew to kepler's laws thus it would essentially stay at the same part of the sky for an earth observer. It is like being on a merry-go-round looking at the center you always look at the same part of the ride ;) However if it was not above the equator but its orbit was inclined then for an earth observer the satellite would be moving in a figure of 8 fashion in the sky. So for us to have stationary dishes and not needing to track the satellite we place them conveniently over the earths equator, or more scientifically with an orbital inclination of 0 degrees.

An interesting fact is that this orbits were firstly discovered by the pronounced Brittish science fiction writer and physicist Arthur Clarke (Space odyssey 2001 etc) back in 1945. Thus the imaginary belt where these satellites are placed is called the Clarke Belt.

Answer 2

No all man-made satellites are directly above the equator. In fact, only a few are there. Some have orbits that go over the poles -- see the first link below.

The reason some satellites are put over the equator, at the "geosynchronous" height, is because at that height, the satellite takes 24 hours to circle the earth. At the same time the earth also takes 24 hours to go around once. So --- the satellite and the earth stay synchronized; the satellite is always over the same spot on the earth.

This what the satellite owners want, if the satellite is broadcasting TV signals to people down below.

Yes, it is related to Kepler's 3rd law, and all the other orbital laws.

P.S. actually, the satellites are not exactly over the equator. They drift back and forth, mostly north and south, a few miles.

Answer 3

Only geosynchronous satellites are useful above the equator.
A satellite in a polar orbit of say 250 miles would eventually cover all areas of the earth.
The earth rotates inside the orbit of a satellite so it"s easy to imagine the relation ship to positions on the ground

Answer 4

I guess its something to do with that from the equator you can get the best coverage for photos or signals from the equator because it veiws easily Europe, most of asia and the Americas! Also, I believe what I read to be interesting based on a relativly unknown scientist saying that gravity is more powerful around the equator due to some unknown effect!

Answer 5

That's only true for geostationary satellites - those that you want to appear in the same place in the sky above the earth for TV, communications and weather purposes.