A geostationary satellite is an Earth orbiting satellite, placed at an altitude of approximately 35,800 kilometers directly over the equator, that revolves in the same direction the earth rotates (west to east). At this altitude, one orbit takes 24 hours, the same length of time as the Earth requires to rotate once on its axis. The term geostationary comes from the fact that such a satellite appears nearly stationary in the sky as seen by a ground-based observer.

A single geostationary satellite is on a line of sight with about 40 percent of the earth's surface. Three such satellites, each separated by 120 degrees of longitude, can provide coverage of the entire planet, with the exception of small circular regions centered at the north and south geographic poles. A geostationary satellite can be accessed using a directional antenna, usually a small dish, aimed at the spot in the sky where the satellite appears to hover. The principal advantage of this type of satellite is the fact that an earthbound directional antenna can be aimed and then left in position without further adjustment. Another advantage is the fact that because highly directional antennas can be used, interference from surface-based sources, and from other satellites, is minimized. Because of this, the geostationary satellites have a lot of applications both in the civil and military areas.

The Space Alliance GEO APP is an interactive visualization tool for geostationary satellites. The database contains information about all the current active satellites in Earth’s orbit including the name, the ID, the launch date, mass, orbital slot, operator, country of origin, expected lifetime etc. To run the tool select a satellite either by directly entering the longitude, the name or the ID (in case you know one of the three) or by using the longitude sliding bar.

If you want to run in Google Earth mode (instead of the default Google Maps), tick the 'Switch to Google Earth' radio button. If you want to see your position compared with the sub-satellite point thick the ‘Show user position’ radio button (this is useful in case of computing the visibility angle, a future option which will be implemented in the GEO APP). If you want to view the elevation from a different point on Earth (future enhancement), manually type the location using the latitude and longitude. The satellites position will be displayed as an icon on the screen. Click the desired satellite icon and a pop up window displaying all the information contained in the database will appear.