Earth's Moon

The Moon at Last Quarter Phase
Credit: NSO

The Moon, also called Luna, is the Earth's only natural satellite. It is the fifth largest Moon in the entire Solar System.

Exploring the Moon

The Moon the only natural object beyond Earth that humans have visited. In 1969, the astronaut Neil Armstrong climbed out of the Apollo 11 landing craft and became the first person on the Moon.

Test your knowledge of the Apollo missions with our Apollo Anniversary quiz.

Unlike the Earth, the Moon has a very thin atmosphere, which does not contain enough oxygen for people to breathe. The surface temperature can be as low as -170 °C at night and climb 120 °C in the day. You can see why visiting astronauts needed such cumbersome spacesuits for protection! 

The Moon is 3,474 km from one side to the other (its diameter). This is about a quarter of the diameter of the Earth. The distance from the Earth to the Moon is about 384,400 km. You could fit 30 planet Earth's between us and the Moon!

The gravity on the Moon's surface is about 1/6th as strong as Earth's gravity. This is because the Moon has a smaller mass than the Earth. You can explore different strengths of gravity in the Solar System with our Gravity Simulator!

Features of the Moon

The Moon has a synchronous rotation. This means that, over time, tidal forces have slowed the rotation of the Moon so that its rotation and orbit are about the same length of time. The result is that the same side of the Moon is always facing the Earth. The only way to see the far side of the Moon to send a spacecraft or satellite.

At any moment we can only see half of the Moon from Earth. But, over a lunar month, we actually see slightly more than half of the Moon's surface - about 59%. This is because of a process called libration. 

Look carefully at the Moon's surface. You will see that it's covered with round craters. The impacts of meteors over many millions of years made the craters. You will also notice large areas that look dark and smooth. These are called Maria (the Latin word for Seas) because early astronomers thought that they were old oceans. We now know that they are regions of solid lava, leftover from when the Moon was much younger and hotter inside. The bright highlands of the Moon contain mountains. Mountains on the Moon are not made by the same geological processes as mountains on Earth. Lunar mountains are the remains of high crater rims made by the impacts of huge asteroids. 

Beneath its surface, the Moon has a core, mantle, and crust. The Moon's dense metallic core is much smaller than the Earth's. The Moon's mantel tells us that the Moon was once a great ocean of magma.  As the magma ocean began to cool, crystals began to form within the magma. Denser crystals sank down to the bottom of the ocean. Lighter crystals floated to the surface to form the Moon’s crust. Scientists think that the crust is thinner on the side of the Moon facing the Earth, and thicker on the side facing away.

How did the Moon form?

Scientists think that the Moon formed during a collision between the Earth and another small planet, about the size of Mars. This is based on lots of evidence, including rocks returned to Earth by the Apollo astronauts. The impact resulted in a cloud of debris orbiting the Earth. This collected together to form the Moon.

Find out more about the Moon, including its orbit, phases and effect on Earth's tides