The Moon, Our Neighbour

The Moon is Earth's only natural satellite — a giant ball of rock that travels around our planet. It is the brightest object in our night sky. Even though it looks small, the Moon is about a quarter of the width of Earth, which makes it surprisingly large compared with the planet it circles.

The Moon takes about 27 days to travel all the way around the Earth. Here is something curious: it also takes about the same time to spin around once. Because of this perfect match, the Moon always shows us the very same face. Nobody on Earth had ever seen the 'far side' of the Moon until a spacecraft photographed it in 1959.

The Moon seems to change shape during the month. These shapes are called phases. The Moon isn't really changing — we're just seeing different amounts of its sunlit side. Half of the Moon is always lit by the Sun, but as the Moon moves around us, we see that lit part from different angles.

After the Full Moon, the lit part shrinks again, moving back through half and crescent shapes until it disappears at the next New Moon. The whole cycle, from one New Moon to the next, takes about 29 and a half days — which is roughly where the idea of a 'month' comes from.

The Moon has no air and no water, so nothing grows there. Its surface is covered in grey dust and dented with bowl-shaped holes called craters, made by crashing space rocks. With no wind or rain to wear them away, craters can stay almost unchanged for billions of years.

On the Moon, gravity is much weaker than on Earth — only about one-sixth as strong. That is why the Apollo astronauts could bounce along in great floating leaps, even though their spacesuits were heavy and bulky.