The orbit of a spacecraft around the Earth can be in the shape of a circle or an ellipse. An artificial satellite in a circular orbit  travels at a constant speed. The higher the altitude, however, the lower the speed relative to the surface of the Earth. Maintaining an altitude of 35,800 km (22,300 mi) over the equator, a satellite is geostationary. It moves in geosynchronous orbit, at exactly the same speed as the Earth, so that it remains in a fixed position over some particular spot on the equator. Most communications satellites are placed in such orbits.

         In an elliptical orbit, the speed varies and is greatest at perigee (minimum altitude) and least at apogee (maximum altitude). Elliptical orbits can lie in any plane that passes through the Earth's centre. A polar orbit lies in a plane passing through the North and South Poles-that is, it passes through the axis of rotation of the Earth. An equatorial orbit is one that lies in a plane passing through the equator. The angle between the orbital plane and the equatorial plane is called the inclination of the orbit.

         The Earth rotates once every 24 hours under a satellite in a polar orbit. A polar-orbit weather satellite, carrying television and infrared cameras, can thus observe meteorological conditions over the entire globe from pole to pole in a single day. An orbit at another inclination covers a smaller portion of the Earth, omitting areas around the poles.
As long as the orbit of an object keeps it in the vacuum of space, the object will continue to orbit without propulsive power because no frictional force slows it down. If part or all of the orbit passes through the atmosphere of the Earth, however, the body is slowed by aerodynamic friction with the air. This causes the orbit to decay gradually to lower and lower altitudes until the object has fully re-entered the atmosphere and burns up, like a meteor.

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