Satellite: Definition & Uses

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  • 0:01 Definition of a Satellite
  • 0:55 Natural Satellites
  • 1:32 Artificial Satellites
  • 2:33 Uses of Satellites
  • 3:15 Lesson Summary
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Lesson Transcript
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.

In this lesson, you will learn what a satellite is, the distinction between natural and artificial satellites, and some of their practical uses. A short quiz will follow.

Definition of a Satellite

If you've ever used a GPS in your car to help direct you from one place to another, you've relied on the information from a satellite. Maybe you've pictured a satellite as a piece of technology floating around the earth, sending information back down to us. But, did you know that the moon is a satellite as well?

A satellite is an object that is in a consistent and stable orbit around a body, usually a planet. There are two main types of satellites: natural satellites, like the moon, and artificial satellites that humans have launched into orbit around the earth.

The earth has one natural satellite (the moon) and an estimated 3,600 artificial satellites. Humans have launched around 6,600 satellites, many of which have been returned to Earth or crash landed. Only about 1,000 artificial satellites are currently believed to be operational.

Natural Satellites

The solar system has a total of 173 known natural satellites. Most planets have many moons, but only a few of them are large enough to have a fairly spherical shape. Earth has one such moon, Mars has two, Jupiter has four, Saturn has nine, Uranus has six, and Neptune has three. There are other moons that are orbiting asteroids, but only two of them are spherical. Examples of moons you've probably heard of are Europa (orbiting Jupiter) and Titan (orbiting Saturn). Cases have even been made that life could exist in the liquid ocean beneath Europa's frozen crust!

Artificial Satellites

The world's first satellite put in orbit by humans was called Sputnik 1, and it was launched in 1957, by the Soviet Union. Since then thousands have been launched, the most significant and well-known being the International Space Station. Artificial satellites have been launched by 10 countries, though a total of 40 countries have been involved in building them. They are launched by rockets in most cases, leaving vertically from the earth's surface. The casing usually falls back to Earth once the satellite is deployed.

There are currently at least 500 operational satellites in low-Earth orbit, 50 satellites in medium-Earth orbit, and hundreds more satellites in high-Earth orbit. The main reason we have satellites so far out is so that they can be in geostationary orbits—meaning they always orbit above the same part of the earth. This is useful for satellite television and communication. They must be at around 36,000 kilometers to achieve this.

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