Eli5, why does the moon appear larger earlier in the night, when it’s “rising” as opposed to later in the night when it’s higher in the sky?



Eli5, why does the moon appear larger earlier in the night, when it’s “rising” as opposed to later in the night when it’s higher in the sky?

In: Earth Science

Because you have something to compare it to.
When it comes over the horizon it is behind a tree or house so it looks big.

When it’s ‘alone’ in the sky it seems smaller because you can’t compare it to anything.

We think its because near the horizon you have known objects to compare its size to.

Its easily testable that it is just an optical illusion and no size change is happening, hold a coin at arms length and it will cover the moon both near the horizon and at the zenith by the same amount.

Your perspective. When the moon is closer to the horizon you have things like trees, houses, water towers, etc. to “compare” it to. When it’s higher in the sky there’s nothing to compare it to.

If you could measure the width of the moon at the horizon (where it appears bigger) and then measure the width when it was higher in the sky, you’d find that the measurements are the same.

ELI5 = It’s an optical illusion.

Perspective. When the moon is close to the ground the horizon forces your brain to percieve the moon as bigger since there are objects on the horizon and the ground as reference points.

Its the same principle as when you feel like your moving faster when driving by close objects vs objects in the distance.

Comparison context.

Next to your house it’s huge. In the lonely sky, it’s tiny.

However, it is always the same size.

Answers saying comparing it to something are wrong. It has nothing to do with comparing it to anything or perspective. It has to do with how much moisture is in the air. When looking towards the horizon, you’re looking through more moisture in the air than if you’re looking straight up. At 10 miles straight up, you have very little moisture that goes up past that. But if you look towards the horizon, you’re looking through so much more moisture maybe 50+ miles which magnifies it greater.

Just like when you put your hand in the water and it looks bigger. More water = bigger magnification. That’s why on very very humid days, the sun/moon are very very large at sunset/sunrise than when it’s very dry out.

When the moon is close to the horizon, atmospheric humidity has a magnifying effect on it’s appearance that decreases as it rises into the sky.


As the moon is never “really” that much further away from Earth in it’s orbit, it is the larger distance of “atmosphere” you are peering through to see it low in the night sky that causes the “big moon” effect.

It’s an optical illusion that no one has a 100% good explanation for yet.

If you hold an object of known size up next to The Moon while it’s high in the sky, it doesn’t start looking big again. Atmospheric lensing only makes it look a fraction larger than it really is. No where close to how much we overestimate its size to be while close to the horizon.

We really don’t know the origin of the illusion.

Your question seems to imply that the moon rises early in the night. In fact it rises at a different time every day, generally around 50 minutes later than the day before. Over time it can rise at any time of the day or night.