Why does the sun flatten at sunset?

Any light passing through the atmosphere.

, "refraction" phenomena occur, including sunlight, moonlight, and starlight.

Refraction refers to the phenomenon that when light is obliquely emitted from one medium (such as water) into a second medium (such as air), part of the light at the interface deviates from the original route and becomes angular to the original route.

At dusk or dawn.

Due to the refraction of light rays (the atmosphere is arc-shaped), the angle of refraction of light rays below.

Large, so that the rays from the top and bottom of the sun are brought closer, so the sun appears flattened.

When any light passes through the atmosphere, "refraction" occurs, including sunlight, moonlight, and starlight;

At dusk or dawn, due to the refraction of light (the atmosphere is rounded), the refractive angle of the lower rays is large, so that the rays emitted from the top and bottom of the sun are closer together, so the sun appears flattened.

1.At noon, the sunlight is perpendicular to the ground, and the light is basically not refracted when it passes through the atmosphere, and the angle between the sunlight and the ground gradually decreases after noon, and the refraction phenomenon becomes more and more obvious when the sunlight passes through the atmosphere. So the sunset gets bigger.

2.caused by human visual illusions. The sun itself has not "gotten bigger".

At dusk, when the sun is closer to the horizon, the buildings and landscapes on the ground that are much smaller and darker than the sun become the reference of the sun, and the vast sky becomes the reference of the sun during the day, in contrast, we will feel that the sun at dusk is larger than during the day.

There is a similar example, the white dots on black paper look larger than the black dots on white paper, which is also due to the illusion caused by the different references to the naked eye, as well as the visual expansion of bright colors, which is also the reason why fat people like to wear black dark clothes.

The sun doesn't get bigger at sunset. It's just that after being refracted by the sunset and water vapor, people's feelings become bigger.

That's because of the different references, but the sun is as far away from us as it is at noon and in the evening.

The sun doesn't change, it's just that our perspective changes.

It's because of the problem of atmospheric refraction.

Anyone who has studied optics knows that light is refracted through different media.

The universe is almost vacuum, and refracted into the Earth's atmosphere.

At sunset, the sunlight enters the atmosphere at a relatively oblique angle, so the refractive angle is larger, so it looks like the sun is large.

Not just at sunset, but also at sunrise.

Two reasons: 1. Parallax:

Different times to observe the sun, the reference is different, causing parallax.

At sunset (rising), the reference objects for the human eye to observe the sun are some scenery on the ground, such as: trees, houses, mountains, fields, ......;

At noon, the reference object for the human eye to observe the sun is the sky.

The trees, the houses, the mountains, and the fields are much smaller than the sky.

2. Lens effect:

There is an atmosphere on the surface of the earth, and the atmosphere is spherical.

Observing the Sun at sunset and observing the Sun at noon is different from the atmosphere through which the line of sight passes. This is equivalent to an optical lens.

Regarding this issue, the "Two Children's Debate" first appeared in "Liezi".

The story tells that when Confucius was traveling to the East to study, he saw two children arguing, and Confucius asked them the reason for the argument. One child said, "I think the sun is close to people when it comes out, but far away at noon."

Another child thinks that the sun is far away when it first comes out and close at noon. A child said, "When the sun first comes out it looks like a big round canopy, and at noon it looks like a plate or a bowl.

Another child said, "The sun has just come out and it is cool and cold, and when it comes to noon, it is so hot that it is like reaching into hot water." Isn't this just the feeling of being hot when you are close and the feeling of being cold when you are far away?

Confucius could not determine who was right and who was wrong. The two children laughed and said, "Who says you know a lot of things?"

This story was made up, and it was used by Liezi to ridicule Confucius's ignorance. In fact, the questions raised by the two children are also the questions raised by Liezi. This question cannot be solved by Liezi. Because this was a problem that people at that time simply could not solve.

Now we know that the average distance between the Earth and the Sun is 149.6 million kilometers. Although there is a difference between the distance between the sun and the earth in the morning and noon, the difference is so small as the distance between the earth and the sun that it does not produce changes in the size of the sun or the heat or cold that we perceive.

So why is the morning sun big and round, while the midday sun looks much smaller?

It turns out that under certain conditions, people can have an illusion of vision of objects. An object appears larger in the middle of some small objects, and an object appears smaller in the middle of some larger objects. It's the same with looking at the sun.

Because in the morning, the sun is rising, and people use the ground objects as references, so the morning sun looks big and round. This is also true for the evening sun to appear larger, but the evening sun appears flatter due to the refraction of light. At noon, the sun is high in the sky, with the sky as the background, and there is no other reference, so it looks smaller.

Also, we look at a white figure that is larger than a black figure of the same size. This is called "photoosmosis" in physics. When the sun rises, the surrounding sky is dark and gloomy, so the sun appears bright.

At noon, the sky is bright all around, and the difference between the brightness of the sun and the backing is not so great, which is why it looks like the sun is bigger in the morning than at noon.

As for the change of heat and cold, it is not caused by distance or proximity. Noon is hotter than morning because the sun shines directly on the ground at noon, while the morning sun shines obliquely on the ground. When the sunlight is direct, the ground and air receive more radiant heat from the sun at the same time and in the same area than when the sunlight is oblique in the morning, so the heat is the strongest.

So it is hotter at noon than in the morning and late afternoon. Of course, by noon the sun is exposed for a long time, and the ground absorbs a lot of solar radiant heat, which is also what makes the temperature rise. And in the morning, when the sun has just risen, it is naturally not too hot.