How was the Moon formed? How much does it weigh? And how long does it take to get there?
The Moon is Earth’s most familiar companion, the closest astronomical object to the Earth. No other planet has a satellite as large in comparison to its own size.
The water on the side of the Earth closest to the Moon is pulled by the Moon's gravitational force. The effect is to make 'bulges' in the water on opposite sides of the Earth.
The Moon has a diameter of 3476 km. This means that you could fit about four Moons across the diameter of the Earth.
The mass of the Moon is 7.35 x 10^22 kilograms, which means the Earth is 81 times more massive than the Moon. This would also mean that someone who can jump up to 5 feet on the Earth could jump 30 feet on the Moon!
The Moon orbits the Earth at a mean distance of 384,000 km. It takes the Moon 27 days to orbit the Earth. Find out more here
It is thought that the Moon formed 4.51 billion years ago - not long after the Earth.
Although the Earth and Moon are both very massive, the Moon is smaller, so its force of gravity is less. Any object on the Moon will weigh about six times less than it does on Earth.
Any early atmosphere that the Moon might have had has escaped from the Moon's feeble gravitational pull.
Because of the lack of any atmosphere the temperature of the Moon's surface varies between -180°C and +110°C. The Moon has little protection from the solar wind, cosmic rays or micrometeorites, and so it is not surprising that there is no form of life there.
The Moon's surface is characterised by light mountainous regions interspersed with dark maria or ‘seas’. The 'Man in the Moon' is formed from patches of these two types of terrain. The maria are vast impact basins which have been filled with basaltic rocks some 3000 million years ago.
Much of the Moon's surface is covered with craters. These are the result of impacts by meteorites. The largest are about 200 km in diameter, the smallest are only about a metre across. Most of these craters were formed between 3000 and 4000 million years ago.
Americans have landed on the Moon six times. The first time was in July 1969 and the last time was in December 1972. Much of our knowledge of the structure of the lunar surface and the geology of the Moon comes from the landings of the Apollo series and the samples of lunar material brought back to Earth.
The phrase 'once in a blue moon' is a familiar one, meaning once in a very long interval of time. A blue moon, by folklore definition, is said to be the second full Moon of the month. However, researchers at Southwest Texas State University have been using historical documents to prove that a blue moon was really a term used by the Maine Farmers’ Almanac to indicate the presence of a 13th full Moon in a tropical year which usually had 12. A tropical year is a measurement of time from one winter solstice to the next.
Read more about blue moons
Learn more about our closest celestial neighbour the Moon in our books published by Royal Museums Greenwich