For as long as humans have looked up at the sky, the moon has been a present feature. It can be bright and appear at times quite large in the sky.
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However, the moon may not be as big as one thinks. On average, the moon is 384,400 kilometres away from the Earth. Compared to the sun, this is relatively close.
Due to its proximity, the moon can look large in the sky. However, the diameter of the moon is only 3475 kilometres wide.
The drive from Canberra to Perth is about 3700 kilometres wide.
When comparing size, the moon and Australia are pretty similar.
If you were to take Australia, and put it 384,000 kilometres away, we'd look similar to the moon - just Australia shaped.
The biggest moon in the solar system is Ganymede, which orbits Jupiter. At nearly 5270 kilometres, it is much bigger than our own natural satellite.
In, fact Jupiter boasts four large moons, called the Galilean moons after they were spotted by Galileo - Io, Europa, Ganymede, and Callisto, each thousands of kilometres wide. Only Europa of this group is smaller than our moon.
However, as astronomers studied Jupiter, more and more moons were found.
Objects like Elara, and other moons were discovered in the late 1800s and early 1900s.
These moons are significantly smaller than the ones Galileo found, ranging from tens to hundreds of kilometres wide.
In the past few decades, dozens more have been found. Not just around Jupiter though, but also Saturn, and they been competing for the title of planets with the most moons.
For the longest time, Jupiter reigned supreme. Then when a new batch of moons were found around both, Saturn claimed the title with 82 compared to Jupiter's 79.
Last year, Jupiter took the title back with a new lot of moons taking its total to 95.
However last week, Saturn re-claimed it - with an extra 62 moons being found, taking Saturn's current tally to 145.
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Just a few years ago, we only thought Saturn had around 60. Its total has nearly doubled. Compare these totals with our one moon, Mars's two, or even the 27 and 14 moons around Uranus and Neptune, respectively, this is a lot.
Why all of the sudden are we finding these new moons? Bigger and better telescopes.
These are allowing us to discover moon that are much smaller that have been previously missed. These new moons are tiny, in some cases only 1 to 3 kilometres wide - smaller than a suburb.
To be a moon there is no real size limit. Objects that are in orbit around another planet or minor planet, such as a dwarf planet, are called natural satellites. Even some asteroids are big enough to have natural satellites on their own.
We call them "moons" as a way to avoid confusion with artificial satellites - the things humans build, and use our natural satellite's name, moon, to avoid the confusion.
As long as you are in a semi-stable orbit around a planet or other object, just not the sun or a star, you can be a moon.
We also have moonlets - even tinier objects that we do not think are moons, but have enough gravity to affect surrounding ice and dust in Saturn's rings. There is no clear definition between each. This is similar to the issue with the definition of a planet - and the eventual debate that led to Pluto's demotion.
The competition, and discussion is far from over, but regardless, there will only ever be one moon - ours.
- Brad E. Tucker is an astrophysicist and cosmologist at Mount Stromlo Observatory, and the National Centre for the Public Awareness of Science at ANU
