A satellite is anything that orbits around a larger object. A natural satellite is any celestial body in space that orbits around a larger body. Moons are called natural satellites because they orbit planets.
Satellites that are made by people and launched into orbit using rockets are called artificial satellites. There are thousands of artificial satellites orbiting the Earth.
The Moon
Any large object that orbits around a planet is called a moon (small ‘m’). The Earth has one moon called the Moon (capital ‘M’). The Moon takes 27.3 days to orbit the Earth once, moving at an orbital speed of 1 km/s.
Find out more about our Moon here.
Moons around other planets
Galileo was the first person to discover that other planets can have moons. He saw that Jupiter had four moons with his newly invented telescope in 1610 AD. At first, he thought they were stars, but he noticed that, each night, the four points of light appeared to change positions slightly. He realised they were actually moons orbiting around Jupiter. Another astronomer of the time, Simon Marius, named them Io, Europa, Ganymede and Callisto after the lovers of Zeus, the ancient Greek mythological King of the Gods and Men. We now know that Jupiter has at least 64 moons.
All except two of the planets (Venus and Mercury) in our Solar System have natural satellites called moons.
Other natural satellites in our Solar System
Planets, asteroids and comets orbit around stars such as our Sun and so can also be thought of as natural satellites. Our Solar System has eight official planets as well as millions of minor planets, asteroids, comets and other objects orbiting around the Sun. All of these can be thought of as natural satellites.
All of these natural satellites are held in orbit by the attraction of gravity between the satellite and the object it is orbiting.