Is the surface of the moon the same size as what astronauts see with the naked eye?

Why does the moon appear so big when it is just rising or about to set? This is the moon illusion, a trick the brain plays on us. Photos prove that the Moon is the same width near the horizon as it is high in the sky, but that's not what we see with the naked eye. So this is an illusion rooted in the way the brain processes visual information. Although we have observed it for thousands of years, there is still no satisfactory scientific explanation.

Go out on a full moon night and find a great vantage point to watch it rise. The moon will make any stargazer take their breath away and say "Wow!" in awe. When we look at the Moon near the horizon, it often appears very large—whether it's rising over a distant mountain ridge or sea, or hanging behind a cityscape, looming behind a dense grove of trees. The truth is: it's all only in your mind. Indeed, the Moon's appearance of being larger is a real optical illusion, rather than being affected by our atmosphere or some other physical aspect. There are many ways you can verify this yourself.

How to confirm the moon illusion?

Put your index finger next to the moon. You will find that the moon is roughly the same size as your fingernail. Or try looking at the moon through a rolled-up paper tube; or bend down and look back through the gap between your legs. Either way, you'll find that the moon isn't as big as it looks.

Another, more reliable way to check the size of the moon is to take a picture of it. Keeping the camera's focus setting unchanged, take a photo when the moon is close to the horizon and when it is high in the sky. Comparing the moons in these two photos, you will find that the two moons are touching each other and have exactly the same width. (The moon in the picture close to the horizon may look a little flat vertically, because the atmosphere acts like a weak lens.)

Photographers can use a telephoto lens to take photos close to the ground. The moon is framed by nearby buildings, mountains, and trees to simulate the moon illusion. So when you see a gorgeous photo of a huge moon, don't forget that this is a distant, near-Earth object captured with a zoomed-in lens. That is, the moon appears larger in these photos only after magnification.

The moon closer to the horizon does look more golden

It is worth noting that there is indeed a difference in the moon closer to the horizon. The Moon tends to have a more golden, even orange, hue when it hangs low in the sky than when it hangs high in the sky. This is because moonlight has to travel a longer distance to pass through the atmosphere and reach people's eyes. As the path length of moonlight increases, the shorter, bluer wavelengths of light are scattered away, leaving more of the longer, redder wavelengths.

(Dust and pollutants also deepen the reddish color)