Forced fluorescence photograph

Why does the moon look so big when it just rises or is about to set? This is the illusion of the moon, and the brain plays a joke on us. The photos prove that the moon is as wide near the horizon as it is at high altitude, but this is not what we can see with our naked eyes. Therefore, 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 an excellent observation point to watch it rise. The moon will amaze any stargazer and sigh in awe, "Wow!" . When we observe the moon near the horizon, it often looks very big-whether it rises on the distant ridge or on the sea, or hangs behind the urban landscape, looming behind the dense trees. The truth is: this is all in your imagination. Indeed, it is a real illusion that the moon looks bigger, not influenced by our atmosphere or some other physical aspects. You can prove it yourself in many ways.

How to confirm the illusion of the moon?

Put your index finger next to the moon, and you will find that the moon is basically as big as a fingernail. Or try to observe the moon through a rolled paper tube; Or bend down and look back through the gap between your legs. Either way, you will find that the moon is not as big as it looks.

Another more reliable way to check the size of the moon is to take pictures of it. Take a picture when the moon is close to the horizon and high in the sky with the camera focal length set unchanged. Comparing the moons in these two photos, you will find that the sides of the two moons are very close and the width is exactly the same. The moon in a picture close to the horizon may look a little flat in the longitudinal direction, because the atmosphere acts like a weak lens. )

Photographers can simulate the illusion of the moon by taking pictures of the moon close to the ground and nearby buildings, mountains and trees with telephoto lenses. So, when you see a photo of Zhang Huali with a huge moon on it, don't forget that it is a distant near-earth object shot after the lens is enlarged. In other words, the moon in these photos looks bigger when enlarged.

20 17 "super full moon" rising over Washington. When the moon moves to the nearest orbit (perigee) from the earth, it coincides with the full moon, and the super full moon appears. Source: NASA/Bill Inges.

The moon near the horizon really looks more golden.

It is worth noting that the moon near the horizon is really different. Compared with when hanging high in the sky, the drooping moon often has a more golden or even orange hue. This is because moonlight needs to travel a longer distance to enter people's eyes through the atmosphere. In the process of increasing the length of moonlight propagation path, those light with shorter wavelength and biased towards blue are scattered, leaving more light with longer wavelength and redder. Dust and pollutants can also deepen the reddish color. )

Why do we have the illusion of the moon?

Be prepared-we really don't know why. You can't say that. It depends on what you think: the news may not be satisfactory, or it may make people marvel at the magic of the brain. But the fact is that although people have observed the illusion of the moon for thousands of years, we still lack a strong scientific explanation.

Generally speaking, the possible explanation should be related to the following key factors: how does our brain perceive the size of objects near or far from us? When an object approaches the horizon, how far do we think it is from us? Our brains don't seem to know that no matter where the moon is in the night sky, the distance between the earth and the moon has not changed much.

Others speculate that objects in front of the moon disturb people's vision and create illusions. Perhaps the trees, mountains and buildings nearby deceived our brains and made us feel as if the moon was actually closer and bigger. An effect called Ponzo illusion discovered a century ago has been explained. Ponzo's illusion describes a scene in which two straight lines extend to a railway track and there are two other horizontal lines with the same length at different distances. Surprisingly, these two horizontal lines don't look the same length. This is because the way the brain processes distance forces you to see such a scene. Is this related to the forced perspective in painting? In the same way.

But this explanation is still not perfect. Nasa astronauts in orbit can see the illusion of the moon, and there are no foreground objects in their sight that interfere with distance judgment. So we still need to work hard to find the reason.

Why not make it beautiful? Although the reason why there is an illusion of the moon has not been fully explained, we still have to say that whether it is true or illusion, a huge full moon hanging high in the sky is indeed a wonderful sight. Therefore, before some people can't figure out what our brains are doing, we just need to enjoy the illusion of the moon and the changeable and unforgettable hazy scenery it brings.