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Space (Universe is expanding (Wave length of waves increase, Red shift,…
Space
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Orbits
Polar Orbit
Satellites in low polar orbit pass over the poles. They orbit between 100 km and 200 km above the Earth’s surface, taking around 90 minutes to make each orbit. The Earth spins beneath the satellite as it moves, so the satellite can scan the whole surface of the Earth. Low orbit polar satellites have uses such as:
monitoring the weather
observing the Earth’s surface
military uses including spying
Geostationary satellites have a different trajectory to polar satellites – they are in orbit above the equator. The height of their orbit - 36,000 km - is just the right distance so that it takes them one day (24 hours) to make each orbit. This means that they stay in a fixed position over the Earth’s surface. Geostationary satellites have uses such as:
communications - including satellite TV
global positioning or GPS - which is used for sat navs (satellite navigation systems)
Geostationary satellites always appear in the same position when seen from the ground. This is why satellite television dishes can be bolted into one position and do not need to move.
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Size of orbit depends on the distance, size of the force, and speed
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A moving object will continue to move in a straight line at the same speed unless a force acts on it. For an object to move in a circle, a force has to act on it all the time.
This force is called the centripetal force. It acts towards the centre of the circle. Gravity is the centripetal force that keeps planets moving around the Sun, and satellites moving around planets.
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