The Moon Illusion

Have you ever wondered why the Moon (or the Sun for that matter) looks huge when it’s low on the horizon, and gets bigger the lower it gets?

It’s called, rather unsurprisingly, the Moon Illusion.

Obviously the size of the moon doesn’t change, but what you might not realise is that this isn’t an optical effect.

It’s nothing to do with angles or “lensing” of the atmosphere or anything else physical.

It’s happening totally in your head.

The easiest way to prove it’s an illusion is to look at the moon through the camera on your phone.

The moon can look huge to your eyes, but take a photo, or just look at your phone screen and it looks a normal size.

It’s just weird.

Another way to prove it’s an illusion is to hold a small pebble,

or even the tip of your thumb,

at arm's length with one eye closed,

positioning the pebble so that it covers the Moon when it’s high in the night sky.

Then, when there’s a huge Moon on the horizon, the same pebble or thumb will also cover it,

revealing that there has been no change in the size of the Moon after all.

Another way to check is to bend over and look at the moon upside down.

Again, it will look normal size

(but you will look pretty strange, which is maybe why this pose is sometimes called "mooning" ? :) )

Anyway...

The Moon Illusion has played on the minds of human beings since at least the time when the Greek Astronomer Claudius Ptolemy wrote about it in the 2nd Century A.D.

The German philosopher Immanuel Kant wrote about it in 1781 in his text “Critique of Pure Reason”, when he said:

"the astronomer cannot prevent himself from seeing the moon larger at its rising than some time afterwards, although he is not deceived by this illusion"

And in 1813, the philosopher Arthur Schopenhauer said that the Moon Illusion is:

"purely intellectual or cerebral and not optical or sensuous."

People have endlessly debated why this might happen

but the truth is that it’s all about perception.

You see, you don’t actually see the world as it is.

Your mind takes the images from your eyes, checks them against your memories, interprets them, decides what the picture is

and then creates a “scene” which you get to experience.

And for some reason your mind can’t cope with the Moon being low in the sky in relation to all the other things going on,

and totally misjudges how big it is,

then shows you a picture with a moon that is hundreds of times bigger than it really is.

Using a phone, or a thumb, or standing on your head, gives you a change of perspective

which lets you see how small the moon is in “reality”.

But here’s the thing…

It’s not just the Moon that this happens with.

It also happens with your problems.

Sometimes your mind misjudges how big your problems are,

just like it does with the moon.

And it will convince you that they’re huge,

when in reality a change in perspective would show you that

they’re much smaller than you believe.

And remember,

if you want someone to show you how small the moon really is,

you know where to find me...