Why is the Moon so big?
Actually, it’s all in your head.
What?!?!?!
Hey Crazies.
Have you ever looked at the Moon when it’s really low in the sky?
It has that reddish-orange color and it looks so much bigger.
The color is a real effect caused by the Earth’s atmosphere.
The light has to pass through more air near the horizon…
and air scatters away the blue half of the spectrum.
The same thing happens with the sun at sunrise and sunset.
but the hugeness of the Moon is a complete illusion.
No, for real, it's all in your head.
It’s called the “Moon Illusion” and it has fascinated humans for a very long time.
To the timeline!
The earliest record we have of the illusion is from a cuneiform tablet that’s been dated
to the time of King Assur-bani-pal in Ancient Mesopotamia.
That’s modern-day Iraq, Syria, and Turkey; but, like, a long time ago!
We also have a record from Ancient China during the time of Confucius
Back then though, people were convinced it was a real effect.
They thought the moon must be physically closer or the optics of the atmosphere must enlarge
the image.
Even Aristotle in Ancient Greece was convinced it was optical
and we all know how his ideas turned out.
It wasn’t until about 1021 CE that someone finally questioned it.
Abu Ali al-Ḥasan ibn al-Ḥasan ibn al-Haytham pioneered the concept of experimentation over
600 years before Galileo making him one of the first actual scientists.
He suggested optics weren’t quite enough to explain the moon illusion.
Why can’t it be a real thing?
Because the Moon’s distance from us doesn’t change very much.
We saw in a previous that the Moon is this far away from the Earth
and because it’s so far away, any changes in its distance will go mostly unnoticed.
Yes, the Moon’s orbit is elliptical, but drawing it like this is misleading.
It looks more like this.
It’s almost circular.
That means, over the course of a month, the Moon’s distance only changes this much.
That’s not that much.
So anytime the news or your friends are like:
Oh my god! It’s a super moon!
It’s actually not that big of a deal.
There’s nothing super about it!
To make matters worse, the moon looks bigger on the horizon, where it’s actually farther away
This is the line you look along when the moon is high in the sky.
But this is the line you look along when the moon is near the horizon.
That's an entire Earth radius farther!
That alone easily cancels out anything optical happening in the atmosphere.
So, what’s really going on?
There are actually several different explanations.
Psychologists treat them like they’re competing explanations,
but, for reasons I’ll make clear later, I think it’s all of them at the same time.
Let’s do this!
First, my personal favorite: the Ebbinghaus Illusion.
Your brain actually changes the sizes of things to add extra contrast.
Take a look at the orange circles in this picture.
The one surrounded by tiny blue circles looks bigger,
but, if you remove the blue circles, you can see they’re the same size.
Even now that you know they’re the same size, you still see them different.
In fact, if I animate one, you see the orange circle change size even though it doesn’t
actually change.
The idea is that a similar thing happens to the Moon when it’s near the horizon.
As the Moon rises, you have a bunch of buildings and trees to compare it to.
so you’re brain’s all like “Wow, that’s really big.”
But, then when it gets higher, it’s surrounded only by the vast emptiness of the night sky,
so it looks smaller.
If you remove everything else from view by, say, looking through a paper towel roll
or even just looking at everything upside down
then the Moon illusion is lessened for some people and eliminated for others.
But, since it’s not eliminated for everyone, we need more explanation.
The second possible explanation is the Ponzo Illusion.
This is an example of something we call “size constancy.”
Basically, our brains know that many things don’t just randomly change size.
So if we see something like a person get smaller, our brains just interpret that as though the
person is moving farther away.
The flip-side is that, if something looks like it’s getting farther away,
but doesn’t change size, then it must be growing.
So the idea here is, as long as we have the same kind of receding perspective
with the sky that we do with the ground, it could happen with the Moon.
When the Moon is near the horizon, it must be farther away,
but it’s always the same size, so your brain thinks it’s bigger
and it changes your perception accordingly.
The problem is that very few people think the horizon Moon looks farther away.
Most people say it looks closer.
Finally, we have the Sky-Dome Model.
Unlike the Ponzo illusion which assumes a flat sky
the sky-dome model assumes a curved sky above a flat ground.
It suggests that maybe our brains map all the really far stuff
like stars and the moon, onto an imaginary dome above our heads.
The advantage here is that it says we connect the sky to the ground at the horizon
and, as a result, underestimate the distance to sky objects.
We saw in the other video that, at best, we can only see about 3 miles in any direction.
That puts the ground horizon in this picture about 3 miles away,
so our brains assume the distant clouds in the sky are also 3 miles away
when those clouds are actually about 10 miles away.
A huge underestimation.
The thing is though, none of these are dramatic enough to explain the Moon illusion.
But if we consider all three at the same time, we might have something.
The Moon illusion is subtle for some and dramatic for others.
A small fraction of people don’t even see it.
Maybe that’s because not everyone is affected the same way by these.
Someone who is greatly affected a lot by all of these, like, say, my Mom,
is going to just be mind blown by the size of the Moon every time.
So, how affected are you by the Moon illusion?
Please share in the comments.
Thanks for liking and sharing this video.
Don’t forget to subscribe if you want to keep up with us.
And until next time, remember, it’s ok to be a little crazy.
In the last video, we learned what was outside the universe.
Comment response time!
WillCant QuickScope asked what aspects of the universe were finite.
As I’ve said in the last couple videos, I would hope all of them, including space.
General opinion among cosmologists though is that space is infinite,
but all they REALLY know is the entire universe is at least 20 times bigger than our observable
universe.
Regardless, let’s just say space is infinite.
Time doesn’t appear to be.
There does appear to be a beginning to the universe.
At least the universe as we know it and time as we know it.
It began 13.8 billion years ago about 380,000 years before this light was emitted.
Speaking of which, several people asked why this was oval and not a circle.
It’s a map projection of the distant universe.
The entire inside of the cosmic horizon sphere, flattened into a plane.
It’s oval for the same reason this map of the Earth is oval.
Bobby Harper asked what aliens would see if they lived on the edge of the universe?
No edge!
The universe is either infinite or it curves back on itself.
Those are your only options.
The universe doesn’t have any edges.
But, if you mean the edge of our observable universe,
they would just see their own observable universe around themselves.
Technically, everyone has their own observable universe around them.
We’re just all a little too close together to notice a difference.
Tooth and Sticks wonders what the difference is between “nothing” and “empty space.”
Empty space is just space and time completely devoid of matter.
Nothingness is a complete lack of even space or time.
Literally nothing!
Gauge Wiley pointed out that Numberphile did a video on how far you’d have to travel
to start finding copies of things.
Spoiler Alert: It’s a long way.
Jonathan Spking wants more Camera Shy Clone.
He is adorable, isn’t he?
I’ll see what I can do.
And, for the last order of business, YouTube is discontinuing normal annotations
on May second this year, which means we’re stuck with that 20-second
mobile end screen, so we’re now forced to separate the comment
responses into their own videos.
The last video was a trial run and the response seemed pretty positive.
This video we’re back to the old end screen one last time
because I felt like you deserved a little warning.
Ahhhh!
Change!!!
Look, I don’t like change either, but maybe I’ll get to respond to more comments?
or at least more detailed responses to the same number of comments.
Anyway, crazies, thanks for watching. See you next time!
What a beautiful Moon tonight.
That’s no moon!
That’s a space station!