A satellite can be defined as any object, either manmade or naturally occurring, that orbits around something else. For example, the moon orbits around Earth, so meets this definition. The Earth is a satellite of the sun. Other naturally occurring examples include comets, stars, asteroids, and other planets.
Orbit is determined by the gravitational pull of the object around which the other body circles. The thing around which a satellite circles is called the primary object. Primary objects are also affected by their satellites, however, and feel some of their gravitational pull. In some cases, when two objects have a similar size and mass, and a similar gravitational pull, they may be called binary systems. Some argue that the moon Charon and Pluto represent a binary system instead of a primary object and satellite, since both have similar mass.
Most are more familiar with the term in relationship to the many satellites that circulate the earth. Sputnik was the first artificial satellite, launched in 1957 by the Soviet Union. The launching of Sputnik is almost analogous for the beginning of the Space Race that followed between the US and the USSR. In today’s climate, however, many countries have found that a cooperative effort is more successful in space exploration and studies. The International Space Station, which orbits earth, is currently the largest manmade satellite in Space, and represents the cooperative effort of numerous countries.
Manmade satellites are classified by types, and there are over ten types. Some of the main types used today include astronomical, communication, Earth observation, and weather satellites, and space stations. Others include those used to monitor Earth from a military standpoint, and biosatellites, which may carry animals or other lifeforms for the purpose of research on earth lifeforms in space. Navigational satellites are now popular and form a vital part of the global positioning system (GPS) now available in many cars.
These objects may also be classified by the height at which they orbit earth or another body. A low Earth orbit satellite circles the planet at a height of 0 to 1,240 miles (1,995.59 km). High earth orbits can be as far away as 22,240 miles (35,791.81 km). Medium earth orbits represent the distance in between high and low earth orbits.
Further distinctions exist to describe the type of orbit it has; for example, Pluto has a slightly elliptical orbit. It may also be classed by what primary object it orbits. A satellite that circles the Earth has a geocentric orbit, for example. The Earth and the planets in this solar system are classed as having a heliocentric orbit since they circle the sun.
A manmade satellite can serve many purposes. People currently use many different systems to track things like weather, to make cellphones work, to find out how to get somewhere, and to gather more information about Earth and about the galaxy. About 5,000 manmade satellites currently orbit earth, and on clear dark nights, it’s often possible to see one in the night sky. Of course, the planets, stars, and comets are also satellites. People should also remember that Earth is not stationary in the sky, as it orbits the sun.