As CSIRO helps track NASA’s Artemis II lunar fly-by mission, we have collated answers to the most asked questions about the Moon by visitors to the Canberra Deep Space Communication Complex.
CSIRO will bring you the questions and answers daily.
What is the surface of the Moon like?
Over billions of years, with very little atmosphere to protect it, impacts from meteoroids and comets have turned the Moon’s surface into a mess of rocky debris.
Much of the debris is a fine powdery dust called lunar regolith.
Moon rocks are another key feature. During the Apollo missions, 50 moon rocks were brought back to Earth.
Outside the USA, the largest rock on public display that was collected by Apollo 11 astronauts is at the Canberra Deep Space Communication Complex.
It has a lot of holes and is sparkly! This is because it is made of basalt and rock glass.
The basalt started out as lava, which contained gases that expanded to form bubble cavities. It cooled rapidly, preserving the bubble cavities as the ‘holes’ we see in the rock.
Rock glass is formed in the high temperatures and pressures experienced at the instant of meteorite impact. These impacts cause rock to instantaneously melt and splash like mud from a puddle onto surrounding rocks.
Testbeds like CSIRO's In-situ Resource Utilisation Facility enable engineers to test technologies headed for the Moon in similar dusty and rocky conditions.
Later Artemis missions will aim to bring back moon rocks to help us understand more of the Moon’s composition.
What is the temperature on the Moon?
Although it looks bitingly cold on the Moon that’s not always the case.
The temperature range between night and day is enormous. When lit by the Sun, the surface of the Moon reaches 127oC. Once night falls, that temperature plummets to about -173oC – near the point when oxygen becomes a liquid (-183oC)!
One of the Moon’s craters never gets any sun, making it a chilly -249oC and the coldest place in our Solar System. The range is so big because unlike Earth, the Moon has very little atmosphere, leaving it unprotected from the Sun’s heat and the coldness of space.
How big is the Moon?
The Moon is bigger than Pluto, but smaller than Australia – though it depends on what you’re measuring.
The diameter of the Moon is smaller than the width of Australia: Perth to Brisbane is 3606 kilometres; while one side of the Moon to the other is 3474 km. Poor Pluto is merely 2377 km across.
However, the surface area tells a very different story. Australia is about 7.69 million km2 whereas the Moon, as a sphere, has a surface area nearly five times bigger at 37.94 million km2. Poor Pluto is again much smaller than the Moon with a surface area of only 17.74 million km2.
Is the Moon actually drifting away from Earth? Why?
If you aim for the Moon, you need to aim a little higher every year. The Moon is drifting ever so-slowly away at a rate of 3.8 centimetres a year. When you consider that the moon sits roughly 385,000 kilometres away that’s a very small amount – around 0.00000000987% a year.
The drift is due to gravity and what’s called tidal pull. The Moon’s gravity influences tides, but because Earth spins more quickly it creates a bulge in our oceans. The bulge pushes the moon into a slightly higher orbit.
How far from Earth have the Artemis II astronauts travelled?
The Artemis II astronauts have travelled further from Earth than any other human in history. At their furthest, they were 406,771km from home. That’s the equivalent of:
- Circling Earth 10 times
- Crossing the Sydney Harbour Bridge 353,713 times
- 2,378,777 MCGs from end to end
- Travelling from Australia’s northern tip (Cape York) to Tasmania’s southernmost point (South East Cape) 110 times
- Or 102 times from Steep Point in the west to Cape Byron in the east.
What is on the “dark side of the Moon”?
The dark side of the moon is not dark at all.
However, because of what’s called tidal locking, one side of the Moon permanently faces Earth. The other, more accurately called the far side of the Moon, always faces away. Each side has roughly two weeks of daytime, followed by two weeks of night.
So, what is tidal locking? The Moon takes 28 days to complete one orbit around Earth. It also takes 28 days to complete one rotation on its axis. This keeps one side of the Moon always facing away.
The dark side of the Moon technically receives more light, because the side that faces Earth is sometimes covered by our shadow (a lunar eclipse).
The best-known feature on the far side is the South Pole-Aitken Basin. More than 2,400 kilometres across and 13 kilometres deep, it is one of the largest known craters in our Solar System.
The Moon was the only known moon until Galileo Galilei discovered four moons orbiting Jupiter in 1610. We now know of 891 moons in our Solar System and keep finding more.
Why does the Earth have a Moon?
Scientists believe the Moon formed from the debris of a collision between the early Earth and an object the size of Mars about 4.5 billion years ago.
To put it in perspective, the Moon is roughly one quarter the size of Earth and Mars is around half the size of Earth.
Scientists even have a name for the object that hit Earth. Theia was a proto planet – essentially the early stages of an unformed planet, made up of a swirling mass of matter.
The Theia Impact (or Giant Impact) Hypothesis is supported by the make-up of Moon’s elements, mirroring those of Earth, but in different proportions.
Why can we sometimes see the Moon during the day?
We can see sometimes see the Moon during the day for the same reason we see it at night.
What we are seeing is the reflection of sunlight off the surface of the Moon. Because the Moon is so big (roughly one-quarter of the size of Earth) it reflects a lot of light, which can still be seen even when the Sun is out.
Stars are much further away, so their light appears dimmer and is easily ‘outshone’ by the Sun in daylight hours.
Think of the stars like a small LED outside while the Moon is more like a spotlight. You’ll notice both switched on at night, but only the spotlight in the day.
Why do some planets have more than one moon?
To have a moon (or in Saturn’s case 274 moons), planets need to be big enough to have a strong gravitational pull. Because the Sun is the biggest object in our Solar System, it has the strongest pull, so planets further away tend to be able to keep more natural satellites in their system.
Mercury and Venus, which are closer to the Sun than Earth have no moons. We have one. Mars has two, Jupiter 95, Saturn 274, Uranus 28 and Neptune 14.
In Earth’s case, the Moon is thought to have been formed by a giant collision. But scientists believe moons around other planets may have been passing by when they were ‘captured’ by the planet’s gravitational pull.
Why is it called the Moon?
The name comes from the old English word mōna which referred to the measuring of time and also gives us the word ‘month’.
Ancient Romans referred to it as Lune, which is why we have so many lunar references.
The French still refer to the Moon as Lune, and in Spanish and Italian it is Luna. Around the world, there are lots of other names for the Moon.
It is Måne in Swedish, Norwegian and Danish, Chandrama in Hindi, Tsuki in Japanese. And in Swahili it is called Mwezi.
CSIRO, Australia’s national science agency, is supporting NASA’s Artemis II mission using its specialist spacecraft communication and tracking expertise.
This includes managing NASA’s Canberra Deep Space Communication Complex, one of three deep space stations around the world that will help NASA stay connected with the astronauts on their journey to the Moon and back.