Humanity has long been fascinated by the Moon. It affects our tides on Earth and in the past has influenced our calender (the word "month" comes from the word "moon").
The Moon is not a planet but a satellite of Earth's, our only natural one.
Some astronomers class the Earth and Moon as a double planet as other planets have moons that are substantially smaller than ours (with the exception of Pluto).
There is no atmosphere on the Moon. It may have had one at some point but its gravity was too weak to keep hold of it. Astronauts measured moon quakes during their visits but these are mild compared to Earth's and are caused by the tidal forces of our planet. Solar wind and the extreme hot and cold temperatures may have an erosive effect on the surface but otherwise scientists consider the Moon to be a dead world.
In this section you will learn about the Moon's size, orbit, features, phases, gravity and mass.