When you look up at night, you might see our Moon glowing in the sky. But did you know that other planets have moons too? A moon is any object that circles around a planet instead of circling the Sun.

Earth has just one moon, and we simply call it the Moon. It travels all the way around Earth about once a month. Our Moon is the brightest thing in the night sky and helps light up the dark.

Some planets have many more moons than we do. Jupiter and Saturn each have dozens of moons circling around them, like a busy crowd of little worlds. Scientists are still finding new ones with their powerful telescopes.

Moons come in all different sizes. Some are tiny lumps of rock no bigger than a mountain, while others are huge. Jupiter's moon Ganymede is even larger than the planet Mercury, which makes it the biggest moon in the solar system.

Moons can be very interesting places. One of Saturn's moons is covered in ice, and scientists think there might be an ocean of water hidden underneath. That makes moons exciting spots to search for clues about life.

The rocky planets have few moons or none at all, but the gas giants have lots. Studying moons helps scientists learn how planets and their families formed long ago.