Why do Satellites in geostationary(parking) orbits, made to orbit the earth at the equator and not at other places?
1 Answer
For a satellite to stay in orbit, it must be moving very fast. The speed required depends on its altitude. The earth is rotating. Imagine a line starting at some point at the equator. At ground level that line is moving right along with the earth at the speed of about 1,000 miles per hour. That seems very fast, but it not fast enough to stay in orbit. In fact, you'll just stay on the ground.
At points farther out on that imaginary line you will be going faster. At some point the speed of a point on the line will be fast enough to stay in orbit.
If you do the same thing about a quarter of the way north or south from the equator (at 45º North or South) you can think of that same imaginary line. At the same altitude and speed there will be a point where you can find a stable circular orbit. However, the orbit is a big circle tilted at 45º and the imaginary line sweeps through a cone shape above the earth. The orbit will move north to south and back again... but at a different rate than the motion of the earth.
Think of the more extreme example of standing directly at the North or South Pole. The imaginary line into the sky isn't going to be moving at all. If a satellite were put in a stationary position directly over a pole, it would just fall straight down. It has to be moving very fast. Orbits can pass over the poles. Orbits which pass over the poles are useful for mapping the planet. On every orbit, the planet turns just a little bit and the satellite will eventually pass over every point on the planet.
