~ Or: If it’s really a paper moon, the red version is my favorite

This isn’t entirely the same as “Objects in the side view mirror may appear closer than they are”.  Except for the part where it is.  Take, for example, the large moon on a full night.

Anyone who knows me knows that I’ve always been kinda fascinated by the moon.  How it looks at difference phases, when it can be seen, how bright it can be, why it’s not made of cheese, and how far that golf ball really did get whacked across its surface.

From as far back as I can remember to middle school science, why the moon looked larger on the horizon was a slam dunk case:

The moon is larger on the horizon because of refraction.  The atmosphere acts as a lens and causes for the moon to look bigger than it is because it is being magnified.  Therefore, the moon – and sun – are of a larger viewable diameter because of that refraction effect.

The end.

So now imagine carrying that notion for most of your life.  Now fast forward to being today-years-old and finding out that the refraction effect of the atmosphere actually has very little to do with the size of objects on the horizon.

Turns out, it’s a trick our brains play on us.  Celestial objects on the horizon are not, in fact, any larger than they are in the sky above us.

Wait ….. what?

When I set out to write this entry, it was going to try to be a fun explanation of the m*th behind how that refraction works and all of the things that go into it.  You know, kinda like the fishbowl effect.

Except it has nothing to do with that refraction and now I am a blubbering mess of lies and deceit.  In fact, I even effectuated the æffirmation of that myth as recently as a couple weeks ago.  So this is now my way of apologizing for saying wrong things.

On with the show!

The Rise and Fall of the Refraction Theory

The notion that refraction and light bending caused by the curvature of the atmosphere goes back more than a couple of moons.

(couldn’t resist that one.  i’ll try to refrain, even though moon puns rock my world)

Greek mathematician and musical theorist Claudius Ptolemy – don’t the Greeks have such FUN NAMES? – wrote in one of his scientific treatises in the second century an attempt to explain the size of the moon on the horizon as being due to atmospheric light refraction.  This theory was then repeated and expanded upon by Greek astronomer Cleomedes (of no known other name.  Kinda like Bono, Drake, Madonna, or Flea) where refraction was a primary cause but also introduced the concept of changes in “apparent distance.”  The concept of apparent distance, it turns out, is going to be real important in just a bit.

But let’s stop for a moment and talk about the refraction theory in more detail.  And then talk about why it doesn’t work.

What exactly is refraction

Refraction, at the most basic level I can think of to describe, is the bending of waves.  Sound and light waves can be bent when passed through a medium, but we’re going to stick to light waves here.

When light passes through something, it changes to some degree.  What we see on our earth planet with our eyes is actually a result of refraction.  Light passing through air changes and we perceive that perception as regular viewing.  Once light enters another medium like, say, water, our perception of what something looks like changes because light waves move slower when entering clear liquids.  Our perception of sound completely changes when underwater and what we hear as sounds are waves.  Light is the same in this case!  Light slows down once it enters water and it looks all kinds of wonky at that point where it looks like it bends an object.

Our understanding of the concept of light hitting different or curved surfaces is not new.  Spyglasses, binoculars, corrective lenses, even our own human eye react to light in different and creative ways.  Our perception of light waves is based on what our eyes see.  Bending that light through lenses can make things look closer or further away.  Corrective lenses will bend the light in a way that allows us to see light waves clearer.

Crazy, isn’t it??

How refraction works in relation to our earthly planet

While the idea that objects in a horizontal position as they are æffected by atmospheric perspective can trick our brains doesn’t impact viewership of the moon, there are aspects of atmospheric refraction that play a role in things we see.

If you’re on a long road trip through Eastern Washington on a hot sunny day and the road ahead of you looks like it’s shimmering as though you missed the only rain storm this month, what you’re looking at is an illusion created by refraction.  This can also be considered to be a mirage.  Not like the kind you see in animated features where off in the distance it looks like there’s a pool and a palm tree and a beverage dispensary and the instant you try to jump into the pool it suddenly turns into sand.  The kind where out in the desert it truly does look like there is water on the horizon.  In the absence of any potable water around, that can certainly seem like an exciting thing to pursue.

But that’s another story for another time.

The mirage of water on the road in this case has to do with differences in hot air density.  The hot air over the scorching road compared to the air surrounding it causes light to refract when passing through it.  The end result is a shimmering effect that looks like water and a sudden panic moment where you’re going to slip on the pavement because your tires are bare and need replacing.  This is not the case.  You’re not going to slide.  You probably should get your tires replaced though.  Just saying.

Why refraction can’t explain moon size

Refraction based on the atmosphere of our earth planet does actually have an impact on the way the moon is viewed on the horizon.  However, not in the way that we think and certainly not in the way that we see it.

At the horizon level, the moon is actually a little bit further away from our proximity to it.  If anything, the moon should be perceptibly smaller.

Light passing through from the moon on the horizon to our eyes might make it look different in color.  Yellow, sometimes even dark red like the picture I took that is the header for this post, thicker atmosphere from point A to point B will change that level of perception.  But the size?

It’s a mirage.  An illusion.  The keto-compatible fatty computer made of meat nestled ever so gently within our skulls is playing hilarious tricks on us.  Let’s get to the bottom of that.

Our Eyes are Tricksy and False

Back to the apparent distance hypothesis.

The short version of the trick that our eyes are playing on us has to do with how we perceive objects on the horizon in our normal daily lives.  If the full moon is high in the sky and we look up at it and there aren’t any other objects to compare it against – like, say, a cityscape or a mountain or an actual horizon – then it looks like what we would expect it to look like.  Small and round.

This is where it gets weird.

When our brains receive visual signals of a moon on the horizon, it’s trying to compensate for perspective.  When the moon is viewed at the same time as objects on the horizon, 95% of people on our human earth have brains that are wired to perceive those objects as being larger or closer.  It’s interesting to note that 5% of people do not actually “see” the moon on the horizon as any larger than at its peak height in the sky.

So …. why is this?

The answer is that scientists are not actually certain they can stick in pin in any one thing to explain it.

The moon’s distance does not change that much no matter where it is and, therefore, the size does not either.  Atmospheric refraction does not cause light to bend in a way that would make it look larger after all.

There was a theory that the discovery of the Ponzo Illusion explained the entire thing.  Perspective and anticipated distance can trick our brains into thinking that some objects look larger or smaller than others.  So why wouldn’t that apply to how our brains think the moon is supposed to look when compared to other objects on the horizon?

Guess what?  According to NASA, astronauts in orbit – without the cityscape of downtown Seattle to compare against – also see the illusion of the moon effect.  FROM SPACE.

So, uhh, where does that leave us?

Snap a Picture and Capture the Soul of the Moon

There are tools at our fingertips that we can use to prove that the moon is actually the same size no matter where it is in the sky.

One of those tricks is apparently to turn around, bend over, and look at the moon between your legs.  Supposedly this will undo the trick and you will view the moon in its more conventional size and form as a result.

If you’re like me and the idea of doing Yoga in order to look at the moon sounds nausea-inducing, there are other ways.

The foremost of this is to take a picture.

Similar to the way a microphone picks up sound waves in a completely agnostic way and doesn’t care one bit what your ears think they hear – try recording a guitar amplifier and compare that sound to what you heard and then spend the next forty years trying to unravel why it’s different – Johann Zahn’s “The Camera” will capture images in a way that is completely unimpacted by what our brain is trying to do to trick us.

Close up example

The following picture – also the header for this blog post, makes the moon looks huge.

Close Up Super Moon - Seattle

Close Up Super Moon – Seattle

Why?  It’s all like zoomed in and stᵫff!

Granted, that looks pretty darn cool even as it is.

But get this.  The picture doesn’t do what it looked like to me any justice.

My brain made my perception of the moon seem so much larger than the picture you are looking at showed.

Zoomed out examples

So now let’s contrast that to some pictures taken from further out.

Super Moon Accurate - Seattle

Super Moon Accurate – Seattle

So check this out.  This picture was taken from a zoomed out perspective.  The moon looked to my naked, undressed eyes closer to the image in the zoom.  When I say closer, what I mean to say is that it looked larger than the zoomed in picture above.

Super Moon Accurate - Seattle

Super Moon Accurate – Seattle

The thing was sure bright though!  That part is captured more accurately in the image above.  But the actual size of the moon? It still appeared to be huge!

If you ask 95% of the people who were at Kerry Park on Queen Anne in Seattle that night, they would agree.

Setting the Moon on the Subject

Finding out that refraction isn’t the reason for the moon looking large on the horizon kinda broke me today!  It was totally not what I was planning on writing about when I began this entry but here we are.

Sometimes the swerves, curve balls, and wrenches in our works turn out to be super fascinating.  It certainly doesn’t take away from the effervescence and beauty of our lunar satellite.

May this post serve only as a means to learn more about the effusive beauty that is the moon and how our brains perceive it.  Given that the trickery taking place serves only to enhance the æffecton we have to the face that looks down upon us from afar, really what more is there to know?


Did you know that you can fit all the planets in our solar system in the distance between the Earth and the moon?

I’ll leave you with that mind-blowing stat.

Until next week!

-= george =-



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About the Author

Straddling the line between the arts - voiceover, music composition, session performer, album mixing - and the world of durable medical equipment. Probably should have spent more time playing on the balance beam as a kid instead of obsessing over Commodore 64 games.

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