Friday, December 15

Why Does The Moon Change Shape?

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Whilst we were driving home from the supermarket recently, my son asked “Dad, why does the Moon change shape?” Good question I thought. So what’s the answer? 

Well, the Moon itself doesn’t change shape, it just appears to do so.  It’s how much of it we can see that actually changes. 

The Moon is made mainly of rock and doesn’t produce any light itself. We only see the Moon when the Sun is shining on it. The portion – or shape – of the Moon that we see depends on where it is in its orbit around the Earth. Or, in other words, it depends on its position relative to the Earth and the Sun. 

The Moon orbits the Earth every 29.5 days. This is also the same amount of time it takes the Moon to rotate once on its own axis meaning that the same side of the Moon always ends up facing us down on Earth. When the Sun is setting behind the Moon (i.e. when the Moon is between the Earth and the Sun), the side facing us is predominantly dark and we can only see a small portion of it. As the Moon continues its orbit and eventually reaches the opposite side of the Earth to where the Sun is, the entire side of the Moon facing us becomes lit by the Sun and we can now see a full Moon. 

If you’d like to see more questions commonly asked by children – and the associated answers – feel free to visit my little website: http://www.butwhydad.co.uk. Thanks!

Image source: Microsoft Office Images

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