Written by Manya Pandey, a first-year undergraduate student.
Do you ever feel the moon appears bigger sometimes?
You’re probably experiencing what’s called the moon illusion. It’s a trick our mind plays on us!
Let’s see how.
What’s the moon illusion?
Moon illusion is a phenomenon that makes the moon look bigger when it’s near the horizon, but it’s not really the case. It’s our brains tricking us!
The truth is that the moon is the exact same size every time we see it. But, if we see it closer to the horizon, it seems bigger – because it is lower and you can see it in comparison to many other things, like trees, buildings, etc – this gives us an illusion that it’s closer to the ground and bigger. But, when the moon is high in the sky, it seems smaller because it’s all alone in a vast sky with nothing to tower over – so it looks smaller!
Don’t believe it? Do this…
On a full moon night, find a suitable spot to view the moon low on the horizon (the horizon is the part where the earth’s surface and the sky seem to meet). Put out your thumb and you’ll see you can still cover the moon with it just as you could with a regular moon.
Or, take a picture. You’ll find the moon looks the same, every day when rising, setting, or when it’s on top of you in the sky
Here’s a great video by ASAPScience that explains it quite well:
What does science say?
Scientists have a whole different approach to the matter – they call it an “optical illusion”. Optical illusions are images that confuse our minds. That’s why they look different to us than they really are. Just like the hypnosis swirl, that makes us feel like we are caught in an endless spiral when we’re not.
Most of the prevailing theories deal with how the brain perceives the distance or the size of objects that are nearer or farther away, and how we process the size of objects near the horizon. Maybe it’s just a problem with our brain but it’s beautiful so let’s enjoy it!
It’s something like, what’s called the Ebbinghaus illusion – an optical illusion of relative size perception. Here’s what it is..
It basically is an illusion to explain how our minds work – for example, as seen above- two circles of the same size are placed near each other. While one is surrounded by bigger circles, the other is surrounded by smaller ones – so the orange circle in the left image looks smaller, while the one on the right looks bigger! That’s what basically happens in the moon illusion.
But sometimes the moon is actually big—like the supermoon
Once in a while, the moon gets really close to Earth and if it happens on a full moon night; it seems like a giant pearl in the sky. Such a moon is called a supermoon, and that’s not an illusion, it’s for real!
Supermoons happen once about every 14 months.
Some people don’t see it
Now, this may be news to you, but there are people who can not see the moon’s illusion. While most human brains are hardwired to see the moon’s illusion, some people don’t see it at all. Scientists believe their distance and depth perception somewhat differs from ours.