Space

10 amazing facts about the Moon

Robert Massey, deputy executive director of the Royal Astronomical Society, discusses the Moon’s most extraordinary secretsFriday, January 4, 2019

By Mark Bailey
Look carefully and you can see the International Space Station in silhouette as it transits the Moon.

1. The Moon began with an explosive collision   

“The prevailing idea is that the Moon was formed in a violent event between the proto-Earth – an early-stage Earth that was much bigger than it is today – and an object (labelled ‘Theia’) about the size of Mars,” explains Robert Massey, deputy executive director of the Royal Astronomical Society. “Debris was ejected into space and then coalesced to form the Moon.” Modern research seems to confirm the Moon is made of material from the early Earth’s crust. Dubbed the ‘Giant Impact Hypothesis,’ this collision is believed to have happened 4.5 billion years ago and would have been 100 million times larger than the event which wiped out the dinosaurs.  

2. It used to look much bigger

“The Moon started out around ten times closer to the Earth than it is now,” reveals Massey. “Imagine looking up at the night sky and seeing the Moon 10 times bigger.” Computer simulations suggest the Moon could even have been 12-19 times closer, at a distance of just 20,000-30,000km, compared to 384,000km today. And it is still spinning away. “Because of a transfer of energy from the rotation and tidal bulges of the Earth, the Moon gets 3.78cm further away each year.” That’s roughly the same rate at which your fingernails grow.

Lunar soil is clearly visible on the suit of astronaut Charles Conrad Jr., commander of the Apollo 12 lunar landing mission, America's second successful mission to the Moon.

3. Moon dust smells like gunpowder

“There is a lot dust on the surface of the Moon and the Apollo astronauts found their suits covered in it when they climbed into their lunar modules,” explains Massey. “One astronaut on the Apollo 17 mission (Harrison ‘Jack’ Schmitt) likened its smell to that of gunpowder. The dust caused some astronauts a kind of ‘lunar hay fever.’” The sneezing and congestion took days to disappear. “The good thing is there is no wind to blow it about,” adds Massey.

4. Surface temperatures reach boiling point 

“Because the Moon has no protective atmosphere, the surface experiences extreme temperatures, from incredibly cold on the far ‘night’ side and above boiling on the ‘sunny’ near side,” explains Massey. According to NASA, the Moon’s temperature can span from 123 degrees Celsius to -233 degrees Celsius. Its mean surface temperature is 107 degrees Celsius in the day and -153 degrees Celsius at night.

This crater, called Daedalus, has a diameter of about 80 kilometres. The Moon is vulnerable to crater-causing meteor strikes because it lacks an atmosphere.

5. Those craters can unlock space history

“Without an atmosphere, the Moon is not protected from meteorites, so it is full of craters which really help us to explore the ‘natural history’ of our Solar System,” says Massey. There are 190 identified impact craters on Earth, with many covered by water and vegetation, but there are millions on the Moon – including 5000 larger than 20km in diameter. “Because the surface of the Moon is dormant and it experiences fewer geological forces (like volcanoes or erosion) than Earth, it neatly stores pristine evidence of ancient formations and craters. That makes it a brilliant laboratory or archive to help understand our Solar System.”

6. You always see the same side of the Moon

Just like Earth, the Moon rotates around its axis, but because that rotation lasts about 27 days – roughly the same as the 27.32 days the Moon takes to orbit the Earth – you only ever see one face of the Moon. “This phenomenon is called ‘tidal locking’ or ‘captured rotation’ and it means the other side of the Moon was completely invisible before the Space Age,” says Massey. “Whereas the near side has lunar maria – large, dark plains which often cover impact basins – the far side is more cratered and rugged, with a thicker crust and less evidence of volcanic activity.”

This image shows the Moon's north polar region - India’s Chandrayaan-1 mission discovered water close to the Moon's poles.

7. The Moon causes tidal bulges

“Put simply, tides on Earth are the result of bulges in the water caused by the gravitational forces of the Moon,” says Massey. “Essentially the Moon pulls up water on one side of the Earth, but on the other side, where its gravitational forces are weaker, the water bulges in the opposite direction.” Those bulges move around the oceans as the Earth rotates, causing high and low tides around the globe. “Because tides are also influenced by gravity from the sun, without the moon we would still have tides but they would be smaller.”

8. Scientists have discovered Moon water 

“India’s Chandrayaan-1 mission discovered water close to the poles of the Moon and NASA has found water in the soil,” says Massey. “It’s not much – for one cubic metre of soil you might extract a litre - but it increases the possibility of one day building bases on the Moon.”

This total lunar eclipse happens when Earth lines up directly between the sun and the moon, blocking the sun's rays and casting a shadow on the moon.

9. A lunar eclipse saved Christopher Columbus

“The Nebra Sky Disc, a bronze artefact dating to 1600BC which was discovered in Germany, is the first known human map to include an image of the Moon - and it is a reminder of how much the Moon has influenced human history,” says Massey. “The Moon even saved the explorer Christopher Columbus from starvation.” After consulting his almanac, Columbus used the lunar eclipse of February 29, 1504, to frighten the native Arawak Indians on the island of Jamaica into giving him and his crew food. According to his son Ferdinand, at the sight of the eclipse the Arawaks “with great howling and lamentation came running from every direction to the ships laden with provisions.”

10. Lunar bases are on the horizon

“Although we are centuries off large numbers of people living on the Moon, it is possible we could soon have scientific bases there, similar to Antarctic research stations,” explains Massey. NASA is hoping to return astronauts to the Moon by the late 2020s. “Planetary scientists believe a base could have lots of uses, from improving the search for organic material to establishing a radio telescope which would be shielded from the Earth to better listen for extra-terrestrial signals. The Moon’s surface area is as big as Europe and Africa combined so we have only scratched the surface.”

Moon: Art, Science, Culture by Alexandra Loske and Robert Massey (Ilex Press) is out now, priced £20.

NASA astronaut Randy Bresnik took this image of the rising Moon from aboard the International Space Station.