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Poster of types of optical telescope: Newtonian, Refracting, and Casserian.
Telescopes Poster

SATELLITES: animation of three geostationary satellites orbiting the Earth.

SATELLITES can be natural or artificial (man made). Satellites can be placed in various orbits. At a unique height (just under 35,800 km above sea level = an orbital radius of just under 42,200 km) their orbital speed can exactly match the rotation of the Earth and so the satellite effectively hovers above a fixed point. This is called the geostationary orbit and three silvery satellites are illustrated here in that orbit. The geostationary orbit is shown as a red ring in space. The geostationary orbital plane (pale pink plane) lies in the plane of the equator (red line around the middle of the Earth) and such satellites are often launched from sites close to the equator (by rockets or by the Space Shuttle). A great advantage of such an orbit is that receiving dishes or antennae (one is illustrated here at the latitude of London) can be trained on a satellite. Because the satellite does not move relative to the Earth, the dish does not have to change orientation to keep track the satellite. This makes geostationary satellites ideal as communications satellites and for satellite television broadcast (think of those fixed dishes on houses). Three such satellites arrayed around the Earth provide coverage of most of the planet (although in reality there are far more). In the graphic, cones of electromagnetic radiation (data) are shown emanating from the satellites to illustrate this point of global coverage.

KEY: Earth:







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