Geostationary satellites (or geosynchronous satellites) orbit the equator at the same rate the earth spins, once per day. They orbit at a distance of 35,900 km above an (almost) fixed spot above the Equator on the earth's surface. This positioning allows continuous monitoring of a specific region. It's field of view is covering approximately one third of the Earth's surface.
Geostationary satellites measure in 'real time', meaning they transmit photographs to the receiving system on the ground as soon as the camera takes the picture. A succession of photographs from these satellites can be displayed in sequence to produce a movie showing cloud movement. This allows forecasters to monitor the progress of large weather systems such as fronts, storms and hurricanes. Wind direction and speed can also be determined by monitoring cloud movement.
Satellites in geostationary orbit include the GMS, GOES and Meteosat series. By international agreement, when a satellite reaches the end of its life is is moved to another usually higher orbit to allow the orbital site to be reused.
Polar Orbiting Satellites
WeatherOnline's Meteosat and GOES imagery