How bright does the moon shine?

Moon Day 12
Moon Day 12

My daughter asks lots of questions about the Moon: How big is it? Why does it change shape? How bright does it shine? And this is my attempt to answer all of her Moon questions in one go.

But first, I would like to thank my friend Alex for kindly allowing me to use his wonderful photo of the Moon to illustrate this blog post.

The Moon is a satellite that orbits (travels around) the Earth. We can easily see it in the sky without a telescope because it is close to us in space and about one-quarter the size of the Earth. It’s surface is made of a kind of rock called ‘anorthocite’. At night-time, the Moon appears to shine brightly but really its rocky surface is just reflecting light from the Sun.

The same side of the Moon always faces towards the Earth. We call the side that we can see the ‘near side’ of the Moon. The other side is known as the ‘far side’ or the ‘dark side’.

As it orbits around our planet, the Moon appears to change shape, from circle to half-circle to crescent. This is because of how much of its surface we can see illuminated by the Sun’s light. This diagram of the moon’s phases explains why – it’s all to do with how the postitions of the Earth and Moon change as they move together around the Sun.

But the Moon’s orbit is not a perfect circle, so there are times when it comes closer to the Earth and other times when it moves further away. This short video explains more about how the Moon moves around the Earth.

Did you know that Earth isn’t the only planet in our solar system to have a moon? Out of the eight planets that orbit our Sun, six of them have moons. The NASA website has a list of all the moons discovered so far in our solar system.


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