What is a satellite?
A satellite is any object that moves in a curved path, or orbit, around a larger body. There are two kinds. A natural satellite occurs in nature — the Moon is a natural satellite of the Earth. An artificial satellite is a machine built by people and launched into space to do a useful job.
Key idea
A satellite stays in orbit because the pull of gravity from the planet provides the centripetal force needed to keep it moving in a circle instead of flying off in a straight line.
Types of orbit
The height of the orbit decides how a satellite behaves:
- A geostationary satellite orbits about 36 000 km above the equator. Its period is exactly 24 hours, so it stays above the same point on Earth. This is ideal for communication and weather monitoring.
- A satellite in a low Earth orbit (LEO) is much closer to Earth, travels faster and has a shorter period. Such satellites are used for imaging and for the International Space Station.
Example
Malaysia's MEASAT communication satellites sit in geostationary orbit, so a satellite dish on a house can point at one fixed spot in the sky and still receive a steady television signal.
Uses of satellites
Artificial satellites serve many purposes: communication (telephone, television and internet), weather forecasting, navigation through GPS, and Earth observation such as watching forests and oceans. In Malaysia, satellites help monitor the haze, track the growth of oil palm plantations and give early warning of storms. They have become an essential part of modern life, connecting even remote villages to television and the internet.
Remember
The higher a satellite's orbit, the slower it travels and the longer its period. A geostationary satellite matches the Earth's 24-hour spin, so it appears to stay still in the sky.