Re: OT--Stuff in the Sky

Posted by David, Surrey UK on August 24, 2007 at 06:54:28 from (84.9.75.186):

In Reply to: OT--Stuff in the Sky posted by Broomstacker on August 23, 2007 at 19:24:13:

The ISS is in what's known as low Earth orbit (LEO), just outside the atmosphere. A lot of "remote sensing" satellites are in similar orbits, because they're as close to the ground as possible without burning up, and they can therefore get good photos etc. The orbital period is about 90 minutes so they appear to move across the sky when seen from the ground.

Most communications satellites, like the ones used for satellite TV, are in geostationary Earth orbit (GEO). This is about 22,000 miles up, over the equator. This orbit is chosen because it has a period of 24 hours. As the Earth also turns once every 24 hours, in the same direction, the satellite stays above the same point on the Earth. From the ground it appears to be fixed in the sky. This is useful because it means you can use fixed antennae rather than tracking ones.

David

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