The Moon is the Earth's only natural satellite. We know it as 'the Moon' but scientists sometimes call it Luna. The word 'lunar' means 'relating to the Moon'.
Exploring the Moon
The Moon the only natural object beyond Earth that humans have visited. In 1969, the astronaut Neil Armstrong became the first person on the Moon. He travelled to the Moon as part of the Apollo 11 mission. 12 astronauts, including Neil, walked on the Moon during the Apollo missions.
Test your knowledge of Moon exploration with our Apollo Missions quiz.
The Earth has an atmosphere. We call it air. The Moon has a very thin atmosphere. It does not contain enough oxygen for people to breathe. The temperature on the Moon can be as low as -170 °C at night! But in the daytime it can rise to 120 °C. This is why Apollo astronauts needed spacesuits for protection!
The Moon is the fifth largest moon in the entire Solar System. It is 3,474 km from one side to the other (its diameter). This is about a quarter of the diameter of the Earth. This means 4 Moons would fit side by side across the Earth. The distance from the Earth to the Moon is 384,400 km. You could fit 30 planet Earth's between us and the Moon!
The gravity on the Moon is weaker than on the Earth. It is about 1/6th as strong as Earth's gravity. This is because the Moon has a smaller mass than the Earth.
Features of the Moon
We always see the same face of the Moon from Earth. The only way to see the far side of the Moon to send a spacecraft. This is because the Moon orbits the Earth once in the same time it rotates on its axis once. We call this 'synchronous rotation'.
At any moment we observe half of the Moon from Earth. But, over a lunar month, we see more than half of the Moon's surface - about 59%. This is because of something called 'libration'. Libration occurs because the Moon's orbit is not a perfect circle.
Look carefully at the Moon's surface. You will see round craters all over its surface. The impacts of meteorites over millions of years made these craters. You should also see large dark, smooth areas. These are Maria (the Latin word for Seas). They have this name because long ago, astronomers thought they were old oceans. We now know they are solid lava. The lava is leftover from eruptions when the Moon was younger and hotter inside. The bright, light coloured highlands of the Moon contain mountains. Mountains on the Moon are the remains of high crater rims made during impacts by massive asteroids.
Beneath its surface, the Moon has a core, mantle, and crust. The Moon's dense metal core is much smaller than the Earth's core. The Moon's mantle tells us the Moon once contained a huge ocean of melted rock. We call this melted rock, magma. As the magma cooled, crystals formed within it. Heavier crystals sank down to the bottom of the magma ocean. Lighter crystals floated to the surface to form the Moon’s crust.
How did the Moon form?
Scientists think the Moon formed when a planet the size of Mars collided with the Earth. This happened over 4,000 million years ago. There is lots of evidence for this theory, including in Moon rocks collected by the Apollo astronauts. The huge impact created a cloud of debris around the Earth. This collected together to form the Moon.