A moon, also known as a natural satellite, is a an object in space that orbits a planet or a minor planet. There are 175 moons in our solar system.
A moon is an astronomical object that orbits a planet or a minor planet. Moons are more accurately known as natural satellites to avoid confusion with the name of our own moon. There are 175 known moons in our solar system. The first moons discovered that didn’t orbit our planet were by Galileo Galilei. In 1610, Galileo was observing Jupiter when he noticed that there were four objects moving around it. Until this point, most people assumed the Earth-centric model of our solar system was correct. Galileo’s observations of the natural satellites of Jupiter showed that not every object in the solar system orbited the Sun, as previously thought.
The term "satellite" came from the German astronomer Johannes Kepler in his paper on the moons of Jupiter. The term came from the Latin satelle which means "guard" or "companion". Natural satellites are smaller than the planet they orbit. They are held in orbit by a gravitational force. Most moons are tidally locked to their planet. This means that one side of the moon always faces the planet.
There are different ways that moons are formed. Moons that have a regular, prograde orbits are generally created from the same protoplanetary disk as the planet. Satellites that have an irregular orbits, orbits which are eccentric or retrograde are normally space objects which have been captured by the gravitational of the planet.
The only moon that humans have ever visited is our own. The first human to walk on the moon was American astronaut Neil Armstrong. As well as sending spacecraft to our moon, orbiters have also been sent to study the moons of Jupiter and Saturn. Huygens was a lander mission launch in 2005 which successfully landed on Saturn’s moon, Titan.