Satellites
A satellite, in the broadest sense, means something that orbits the earth. However, the term is usually used to refer to man-made satellites - natural satellites are called moons.
Natural Satellites: Moons
Natural Satellites, or moons are natural objects that orbit planets. The earth only has one moon, however of the 240 moons in our solar system only a few are larger than The (Earth's) Moon.
For reference, below is a diagram, to scale, of the Earth and Moon. It shows the distance between the two and how it is much larger than one might expect.
Artificial Satellites
An artificial satellite is a man-made object that is put into space. Their main use is for communication. And applications include telephone, television and navigation (e.g. SatNav that can be used in cars). There are two types of communication satellite. The first are active satellites which have equipment that allows them to collect and transmit information. Second are passive satellites, which reflect signals from one place on earth to another.
Orbits
Firstly we will look at two types of orbit that are used by satellites, they are geostationary and near-polar orbits:
| Geostationary | Near Polar |
|---|---|
This orbit is about 39 000km above the earth's surface; the satellite orbits at the same speed as the rotation of the earth; this means that it will appear not to move in the sky. This type of orbit is used for most television and telephone satellites because it means that atenna (i.e. your satellite dish) can be pointed in the same direction to recieve the signal |
Satellites on this orbit will travel from one pole to the other and back again several times a day. This means the path it takes over the planet appears as a wave because the earth below it is rotating horizontally whilst it orbits vertically. This orbit is used for mapping the earth and weather satellites because it provides coverage of the entire earth. However, if you need to recieve information from it you have to wait until the orbit is in range, and then the antenna will have to track its position. |
If you need to do some calculations about the orbits of objects then these two equations should come in very handy.
