That moon is fake!

Illustration of a church with a giant full moon behind

You’ve probably seen a photo like the illustration on the left and thought: “That moon must be a Photoshop trick. It can’t be real”.

And yes, there’s a trick — but it’s not Photoshop, and the photo is real… with a few caveats.

Because it’s true: with our eyes, we never see the moon looking that big. So what’s going on?

It’s the magic of the telephoto zoom lens, my friend.

Our eyes are amazing. They work better than the most expensive lens money can buy. They focus at any distance, give us depth perception, and cover a field of view of about 180° (except Sheldon Cooper, who can see his own ears in a good day). Camera lenses don’t work that way: depending on their type, they only cover a certain range of distances.

Broadly speaking, there are three types of lenses: standard, wide-angle, and telephoto.

A standard lens is closest to human vision. Looking through the viewfinder with a standard lens, you’ll see more or less what you see with the naked eye — but with a narrower field of view. For example, a 50 mm lens gives you around 40°, compared to our fantastic 180°. In other words, we see a scene much wider than what fits in the photo.

If you want to capture more of a scene than a standard lens allows — say, for a panoramic view — you’ll use a wide-angle lens, which (as the name not-so-subtly suggests) opens up the field of view. A 14 mm lens gives you about 100°.

Other times, you might want to photograph a lion as if you were close, without actually being close (because you’d like to keep your skin intact). That’s when you need a telephoto lens: it magnifies distant subjects at the cost of narrowing the field of view, like peering through a tube. A 300 mm lens, for example, gives you only about 8°.

If you’re wondering about those mm, that’s the focal length. It’s a way to classify lenses. Standard = 50 mm. Smaller numbers = wide angle. Larger numbers = telephoto. And a zoom lens, whatever its type, lets you adjust the focal length across a range — for example, a 100–400 mm covers everything between those two lenghts. The opposite of a zoom is a prime lens, which has a fixed focal length.

Now back to the photo of the church with that giant moon behind it. If you use a wide-angle lens, you can probably capture the whole building from the square in front of it. But if you choose a telephoto lens and you still want to fit the entire church, you’ll have to step back. A lot. The longer the lens, the farther back you need to go — otherwise you’ll end up with just a piece of the church in the frame.

The problem is, if you only do that, the moon will still look its normal size in the frame — just as small as it looks to the naked eye. So? Am I messing with you?

Here comes the trick

To make the moon look oversized, you need to be far enough away that the object (say, the church) and the moon subtend the same apparent size. What does that mean? It’s how big or small something looks depending on its distance. Take a photo of a person from 3 or 4 meters away, but hold your finger right in front of the lens — suddenly your finger looks as big as the person (and ruins the shot, not that I would know from experience…).

As for the moon, its apparent size is about 0.5°. Out of our 180° field of vision, the moon only covers half a degree. That’s just a complicated way of saying: it looks small, because even though it’s huge, it’s really far away.

So, for our example, we need to step back far enough that the church tower we want in front of the moon also covers 0.5° of our vision. How far is that? Time to bring in some Greek letters.

First, convert 0.5° into radians (because math loves radians):


Then use the formula for angular size, which relates the height of an object (H), its distance (D), and the angular size (θ, pronounced “theta”):

Since we already know the moon’s angular size (0.5° or 0,008726 radians) and the object’s height, we can solve for the distance D:

In practice, it boils down to multiplying the height H of the building by 114 (rounded for simplicity). Let’s say the tower is 40 m tall: 40 × 114 = 4,560 m. So, grab your car keys and find a spot about 4.5 km away with a clear view of the church. Wait there for the moon to rise in just the right spot (that part requires careful planning, but that’s a topic for another article). Now pull out your telephoto lens, zoom in until the church fills up the frame, and voilà: the building looks closer than it really is, and the telephoto magnifies also the moon, making it appear as big as the building.

So now you know: it’s not Photoshop — it’s optics and a bit of applied trigonometry. Next time you see a photo of a giant moon behind a landmark, remember the real trick is math… and getting there early enough to claim a spot among the forest of tripods you’ll probably find.

Note: The opening illustration was generated with Sora AI, based on a photograph by Herbert Heim of the Wallfahrtskirche Unserer Lieben Frau Mariä Heimsuchung in Bildstein (Austria), licensed under CC BY-SA 4.0. The original can be seen on Wikimedia Commons.

Next
Next

Who invented photography?