What Does Geostationary and Geosynchronous Mean?
Learning the difference between a geostationary and geosynchronous satellite helps if one breaks down the words.
“Geo” comes from ancient Greek and means “earth”.
“Stationary”, has its origin in the 1400s and means, as most people know, fixed in one place, not moving.
“Synchronous”, has its origins in the 1600s with Latin and Greek roots and means: occurring at the same time.
So, a geostationary satellite is a satellite that has an orbit that appears fixed in one place relative to a point on the Earth. This type of orbit will only work for satellites that are in a circular orbit, which is in the same plane as that defined by the Earth’s equator. For this to occur, the satellite has to be at an orbital altitude of 22,236 miles (35,786 km). Many weather and communication satellites, including satellite TV and radio are in geostationary orbits, which gives them the ability to cover large areas of the Earth. This also explains why your satellite dish can remain pointed in one direction and does not have to track the satellite it is receiving its signal from.
Note that the author of 2001 A Space Odyssey, Arthur C. Clark, is credited for developing the concept of geostationary orbits in a science fiction story he published in 1945. It would not be for another twenty years before his ideas would be put into practice with the launch by NASA of the communication satellites, Syncom I and II in 1963.
A geosynchronous satellite, or rather the orbit it inhabits is a bit different from the orbit a geostationary satellite occupies. The geosynchronous orbits are not confined to be in the plane of the equator, but are elevated at an angle to the equator. This elevation will cause the satellite to move about the Earth, but it will appear over the same spot on the surface one sidereal day later (23h, 56m, 4s). It is synchronized with the Earth’s rotation, but as opposed to the geostationary satellite, which you would see over head all day long, the geosynchronous satellite will only be over head at the same time each day.
.Also, note that technically, a geostationary satellite is also a geosynchronous satellite since its orbit is synchronous with the Earth’s rotation.
An Orbital Summation
Learning the difference between a geostationary and geosynchronous satellite involves understanding a little bit about geometry and some simple definitions that we are all familiar with. The key is remembering that stationary literally means, not moving, and that will only occur over the equator. There are other orbits beside the geostationary and geosynchronous orbits, such as Low Earth Orbit (LEO), which is where the International Space Station is and Medium Earth Orbit (MEO), which the GPS satellites occupy.
If you are intrigued with the idea of orbits and how they are used to position satellites and travel about the Solar System check out the article: Orbital Mechanics and Interplanetary Travel.