A polar orbit is so called because a satellite in polar orbit passes over the North and South Poles. As it orbits the Earth, the Earth spins on it's axis, once every 24 hours. This means that the satellite passes over a different part of the Earth with each orbit, eventually passing over every point of the Earth. They also orbit rapidly – one orbit every few hours – and because there are a lot of polar satellites in orbit, if a certain part of the Earth needs to be monitored, there will very soon be a satellite in a position to do so.
Satellites in polar orbits orbit quite close to the Earth – only a few hundred miles or so. This and the other features described above makes them very useful for certain tasks.
-
Because of their proximity to the Earth, they can take very clear pictures. This makes them useful for spying and these satellites are used a lot by the world's biggest military powers.
-
They can take pictures of weather systems in detail and are widely used for weather forecasting.
-
They are used for communications – satellite phones etc.
-
The Global Positioning System – GPS – is run using satellites in polar orbits.