Geosynchronous Satellite: Observing Earth From Space

Instructor: David Wood

David has taught Honors Physics, AP Physics, IB Physics and general science courses. He has a Masters in Education, and a Bachelors in Physics.

After completing this lesson, you will be able to explain what a satellite is, describe a geosynchronous orbit, and give some examples of how they are used. A short quiz will follow.

What is a Satellite?

In general, a satellite is a body orbiting the Earth or another planet. These can include natural satellites like the Moon, or artificial satellites that we humans have launched into space.

A GPS Satellite
A GPS Satellite

Humans build satellites for all kinds of reasons: for communication, to send television signals, to spy on other countries, to conduct research, for warfare, and to track weather patterns. We also make them orbit in numerous ways: in polar orbits, geosynchronous orbits, or super-synchronous orbits, to name but a few. There are dozens of types of orbit. Orbits also vary by height above the Earth, from low Earth orbit (100-1200 miles above the Earth) to high Earth orbit (over 22,000 miles). Today we're going to talk about one of the most common ones: geosynchronous orbits.

The Heights of Various Orbits: Black dashes = synchronous; Green dashes = GPS, Red dots = International Space Station; Yellow area = medium Earth orbit; Cyan area = low Earth orbit.
The Heights of Various Types of Orbit

Geosynchronous Orbits

A geosynchronous orbit is an orbit around the Earth that has a time period of one day. More simply, this means that a satellite orbits the Earth once every 24 hours. As a result, it appears at the same place in the sky at a particular time of day. At 11am today it appeared at a certain point in the sky, and at 11am tomorrow it will appear at the same point. The first geosynchronous satellite was called Syncom 2 and was launched in 1963. It was a communication satellite, and it allowed the first satellite telephone call between two heads of state ever made: President John F Kennedy calling the Nigerian Prime Minister. It also was used to attempt the first ever satellite television transmission. Today there are at least 600 such satellites, some of which are no longer being used. In order to orbit geosynchronously, the satellite must be in a particularly high orbit.

Syncom 2
Syncom 2

Geosynchronous satellites are used when you need the satellite to be over the same part of the Earth each day. Because of this, they tend to be used for things like communications, TV signals, weather forecasting, and sometimes defense or intelligence operations.

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