What colour is the moon? Our closest neighbour might not be the colour that you think

The bright, crisp whiteness of the moon is a kind of optical illusion

Andrew Griffin
Tuesday 13 October 2015 11:01
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We see the moon every night — but you might not know what colour it is.

A new video shows how the bright, white colour of the moon that we see is a kind of optical illusion — and that it’s really a much duller, darker grey.

The full moon looks bright when seen from Earth. But it only looks so light because there’s nothing to compare it with — except for the (very dark) sky that surrounds it.

Since our eyes compare the relative brightnesses of what we’re looking at and the things that surround it, the moon appears bright. But if that is put next to anything else, we can in fact see that it’s not bright at all — and the moon only reflects about 13 per cent of the light that hits its surface.

Our eyes need to account for the context of what we’re looking at to ensure that we don’t get tricked by changes in the light. If a car goes beneath a bridge, for instance, we need to account for the fact that the colour of the car hasn’t changed — the light has just got a little darker.

But the effect can also be exploited, as it has been in numerous optical illusions. By tricking the eye into thinking that something is having a shadow cast on it, for instance, we can think that things are different colours when they are in fact the same.

A similar version of it could even be seen in the famous Dress optical illusion — it all depended on how your eyes saw the background, and what your brain thought the colour of the dress should be compared with.

If we could view the moon under normal conditions — in comparison with the Earth, for instance — it would look like a very dark grey.

That same colouring can be seen on the floor in pictures taken on the Moon during the Apollo missions. There, it’s not being compared with the darkness of space but with the bright whiteness of a spacesuit — and so look a much darker grey.

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