What is a satellite?
A satellite is an object (e.g., Moon, planet or machine that orbits a planet or star). For example, Earth is a satellite because it orbits the Sun. Likewise, the Moon is a satellite because it orbits Earth.
The Earth and Moon are examples of natural satellites. In astronomy, the word ‘satellite’ usually refers to a machine launched into space to orbit the Earth or another space object. Thousands of artificial satellites orbit Earth. Some take pictures of Earth to help meteorologists predict weather and track hurricanes, while others take pictures of other planets, the Sun, black holes or faraway galaxies. These pictures help scientists better understand our Solar System and universe.
Most satellites orbiting Earth, however, are used for communication, such as beaming TV signals and phone calls around the world. The Global Positioning System (GPS), a key navigation tool, is a group of more than 20 satellites. If you have a GPS receiver, these satellites can determine your exact location.
Why Are Satellites Important?
Satellites can see large areas of Earth at a time. This enables them to collect more data quicker than instruments on the ground.
Satellites also can see into space better than telescopes on Earth's surface. This is because they fly above the clouds, dust and molecules in the atmosphere, which block certain wavelengths of light from reaching the ground.
TV signals didn't go very far before the advent of satellites. They travel in relatively straight lines and quickly trail off into space rather than following Earth's curve. Sometimes mountains or tall buildings would block them. Making phone calls to faraway places were also a problem. Setting up telephone wires over long distances or underwater is difficult and expensive.
With satellites, TV signals and phone calls can be sent up toward a satellite and almost instantly bounced back to different locations on Earth.
What Are the Parts of a Satellite?
Satellites come in many shapes and sizes. Most have at least two parts in common, an antenna and a power source. The antenna sends and receives information, often to and from Earth. The power source can be a solar panel or battery. Solar panels make power by turning sunlight into electricity.
Many satellites carry cameras and scientific sensors. Sometimes these instruments point toward Earth to gather information about our land, air and water. At other times, they face towards space to collect data from our Solar System and universe beyond.
How Do Satellites Orbit Earth?
Most satellites are launched into space on rockets. A satellite orbits Earth when its speed is balanced by the pull of Earth's gravity. Without this balance, the satellite would fly in a relatively straight line off into space or fall back to Earth. Satellites orbit Earth at different heights, different speeds and along different paths. The two most common types of orbit are ‘geostationary’ (jee-oh-STAY-shun-air-ee) and ‘polar’.
A geostationary satellite travels from west to east over the equator. It moves in the same direction and at the same rate as Earth’s spin. From Earth, a geostationary satellite looks like it is standing still since it is always above the same location.
Polar-orbiting satellites travel in a north-south direction, from pole to pole. As Earth spins underneath, these satellites can scan the entire globe, one strip at a time.
Why Don't Satellites Crash Into Each Other?
Actually, they can. NASA and other international organizations keep track of satellites in space. Collisions are rare because when a satellite is launched, it is placed into an orbit designed to avoid other satellites. But orbits can change over time. And the chances of a crash increase as more and more satellites are launched into space.
In February 2009, two communications satellites - one American and one Russian - collided in space. This, however, is believed to be the first time two artificial satellites have collided accidentally.