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How Are Polar & Geostationary Orbits Similar?

Since the 1950s, countries around the world have launched satellites into space. These satellites transmit signals for television and radio, provide information about weather systems and spy on the military assets of foreign countries. Thousands of these satellites are in orbit around the Earth. The orbits of the satellites, however, differ greatly in altitude, speed and path. Two of the most common orbits for satellites are called polar and geostationary.

Types
- A polar orbit is an orbit that passes over the poles of the Earth. Because a satellite in this orbit must pass close to the poles, it necessarily moves perpendicular to the Earth's equator. The Earth rotates below a polar orbit, making most of the surface potentially visible throughout the day. A geostationary orbit, on the other hand, keeps a satellite locked into one position. This orbit holds the satellite in place over the equator, rotating at the same speed as the Earth itself.
Time Frame
- The rotation period for a satellite in a geostationary orbit is equal to the period of the Earth's rotation: 23 hours, 56 minutes and 4 seconds. A polar rotation period is much faster, typically 100 minutes. A satellite on a polar orbit can therefore circle the Earth many times in a given day.
Size
- To achieve specific orbits, satellites need to be placed at specific altitudes in space. For polar orbits, this distance is most typically 1,000 kilometers (621 miles), since the atmosphere would cause problems with lower-altitude orbits. Geostationary orbits must be much higher than this, at 35,786 kilometers (22,236 miles) in altitude, to maintain an orbit identical to the Earth's rotation period.
Appearance
- Satellites in polar and geostationary orbits differ greatly when observed in the sky. Due to their position above the Earth's equator, geostationary orbits are always found along the celestial equator (the projection of our equator onto the stars). Geostationary satellites do not appear to move from their locations, looking just like stars without the aid of a strong telescope. Satellites in polar orbits, on the other hand, appear to move constantly in the sky. Their path runs from north to south or from south to north, and the satellite passes overhead in a matter of minutes. You have the best chance of seeing any satellite shortly after sunset or just before sunrise, when the satellites most easily reflect the sun's light.
Benefits
- Because they can pass over the entire surface of the Earth in a short time, polar-orbiting satellites are perfect for mapping purposes and for surveillance and spy work. Geostationary satellites are more appropriate for use as television and broadcast satellites, communications satellites and some types of weather satellites.

Astronomy