Why does the moon change shape from a circle at full moon, to a urrr... moon shape, and sometimes disappear all together?
The moon doesn't make any light of it's own, it is just a big whiteish ball of rock. A piece of paper is bright when there is light, but in a deep shadow it will be dark like everything else.
|A picture of a moon buggy on the moon, look how dark the shadows are|
Now a shadow is caused by something getting in the way of the light, so half of the moon is in a shadow caused by the other half.
Now because the moon is going around the the earth you see the shadow from different angles, so you see the moon lit up in different shapes, these are called the phases of the moon.
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|The moon orbiting the earth, with what the moon looks like from earth in the corner - to get exactly this effect you would have to be standing on the north pole, as the moon would be a bit rotated otherwise.|
So basically the moon doesn't change shape at all, its shadow just moves around it.
Thanks to Year 5 and 6 Bryncrug Primary School for pointing out my errors