The weather is fine, why is the sun much bigger than noon in the morning and evening?

The earth's orbit around the sun is an ellipse, and the sun is located in one of the focuses. Every year, 65438+/kloc-0 passes through perihelion (from the sun 14765438+ million kilometers) in early October and perihelion (from the sun 15265438+ million kilometers) in early July. After calculation, when the earth moves from the far day to the perihelion (July ~ 65438+1October) every year, it is about 8000 kilometers away from the sun from morning to noon. During this period, the noon sun is closer to us than the morning sun. On the contrary, when the earth moves from perihelion to apohelion (65438+ 10 to July), the distance from the sun at noon every day is about 8000 kilometers farther than that in the morning. The difference of 8,000 kilometers between the sun and the earth in the morning and at noon is insignificant compared with the average distance between the sun and the earth (65.438+0.5 billion kilometers), which is difficult to observe with the naked eye. It can be said that the sun is as far away from us as noon.

"Sunrise is as big as a car cover and noon is like a bowl", which is due to the visual error caused by human eyes touching objects. In real life, people have this experience: if two circles of the same size are placed in several big circles and the other is placed in several small circles, at first glance, the former is small and the latter is big. According to the "light penetration" function of physics, we always look at the white figure bigger than the black figure of the same size. At sunrise and sunset, there is only a horizon on the horizon, and there are trees and houses nearby. In addition, the surrounding sky was dark at this time, and the sun was particularly bright and big. At noon, the background is a vast sky, and nothing can compare with it. The surrounding sky is already very bright, not much different from the brightness of the sun. So, it looks like the sun is very small.

As we know, ground radiation is the direct heat source of the atmosphere, and the magnitude of ground radiation energy is related to the amount of solar radiation energy received by the ground. In the morning, the sun rises, the horizon is low, and the sun shines obliquely on the ground. The ground absorbs less solar radiation energy per unit area and the temperature is low, so it is still "cool". At noon, the sun shines directly on the ground, and the solar radiation energy absorbed per unit area of the ground increases, and the temperature is high, just like the soup exploration in Japan and China. Therefore, it is wrong to infer the distance of a day by saying "far small near big" or "near hot and far cool".

The first person who questioned it was Belliman of the former Soviet Union. He pointed out in "Interesting Astronomy" that from noon to sunset, the average distance between the sun changes about 7,500 kilometers, which is greater than the distance change caused by the earth's rotation of 6,400 kilometers. He faced up to the fact that the orbit of the earth's revolution is elliptical, and thus reached a new conclusion. In half a year, noon is closer than dusk, and the other half is farther than dusk.

Professor Dai Wensai, a famous astronomer in China, saw Burleiman's new conclusion and thought it was too simplistic to answer all the questions.

This seemingly simple problem is actually very complicated: the earth's orbit around the sun is elliptical, and when passing through perihelion and apohelion (65438+1early October and early July), the distance between the sun and the earth changes from Sunday to 1500 km; At the beginning of April and 10, the distance between the sun and the ground on Sunday can reach 43,000 kilometers; At different latitudes of the earth, the distance change caused by the earth's rotation is different. In the south pole or north pole of the earth, this assertion cannot be established, because the sun is at noon, the sunrise horizon is early, and the sunset horizon is late, and there is no morning or evening; The rotation axis of the earth is not parallel to the common rotation axis, and the included angle is 23.5. Therefore, the time of sunrise and sunset and the height of the sun at noon are constantly changing in a year, and vary with different latitudes.

After considering various factors, Professor Dai Wensai made an accurate calculation and research on this seemingly simple problem. He published a paper "The Change of the Distance between the Sun and Observers in One Day" in Journal of Nanjing University 1955, and then published a popular science article in Guangming Daily 1958+05.

The solution to this problem is different for different latitudes. For Beijing, from 65438+February 15 to 65438+1October 22, the noon sun is closer than the morning and evening; 65438+1October 22-June 5, the sun is farther at noon than in the morning and closer than in the evening; From June 5 to August 1, the sun is closer at noon than in the morning and evening; From August 1 to February 15, the sun is closer at noon than early and farther than late. Among them, 65438+1On October 22nd and June 5th, the distance between the sun and the morning is equal; On August 1 day and February 15, the distance between the sun at noon and at night is equal. This is calculated with the data of 1954, but it can be applied to 100. Even after 100 years, the difference is only one day.

The average distance between the sun and the earth is called an astronomical unit: 149597870km. It can be seen that even if the maximum time-ground distance of Sunday variation is 43,000 kilometers, it only accounts for 2.87/ 10000 of the average distance between the sun and the ground.

Just because the sun looks bigger in the morning than at noon doesn't mean that the sun must be closer to us in the morning than at noon. If we take a picture of the sun in the morning and at noon with the adjusted camera, we will find that they are exactly the same size in the picture. It turns out that when our eyes observe an object, the size we feel depends not only on the actual size of the object itself, but also on the distance, background and brightness of the object itself. In the morning, the sun has just risen from the horizon, and the trees and houses in the distant background are too small to be seen clearly. The sun rises against this background. At noon, the sun hangs high in the vast sky, which is very small compared with the tall trees and houses near the earth.

As for feeling hotter at noon than in the morning, it is because the sun shines obliquely on the ground in the morning and directly on the ground at noon. The atmosphere through which the sun passes in the morning is thicker than that through which the sun shines directly on the ground at noon, so the sun at noon feels strong.

Ice is a symbol of cold, and people will shudder at the mention of it. However, in the cold winter, Eskimos living in the Arctic Circle spent the cold winter in houses made of ice. Do you know why igloos can keep out the cold?

Confucius traveled eastward and saw two children arguing. Ask why. A Children's Day: "When the day begins, I approach people." And Japan and China are far away. "A son is far away from the beginning of the day, and Japan and China are close.

One day: "the sun rises as big as a car cover at first, and rises as a dish at noon." Isn't this a great peace for those who are far away and small? "

One day: "It is cool at the beginning of the day, and the soup is explored in the middle of the day. Isn't this near hot and far cold? "

Hearing this, Confucius could not judge who was right or wrong.

The two children laughed: "Who is Zhihu!"

This story is about the Spring and Autumn Period. Two children asked Confucius, a scholar at that time, "When is the sun near us?" One of them thinks that the sun looks bigger in the morning than at noon, so the sun is closer to us in the morning. The other thinks that the noon sun is warmer than the morning, so the noon sun is closer to us. The two of them came to two completely different conclusions from two different aspects, both of which made sense. Even Confucius doesn't know which is right.

This is a seemingly simple and complicated question, but today, scientists have been able to answer this question completely, in a word; The time of sunrise and sunset and the height of the sun change constantly throughout the year, and change with latitude. From 65438 to 0955, Professor Dai Wensai, a famous astronomer in China, made an in-depth study on this issue and published a paper entitled "The Change of the Day Distance between the Sun and Observers".

Take Beijing as an example. From June 65438+February 15 to1October 22, the noon sun is closer than the morning and evening sun. At noon from June 22nd to June 5th, the sun is farther than the morning and closer than the evening, and at noon from June 5th to August 1 day, the sun is closer than the morning and evening. From August 1 to February 15, the sun at noon is closer than in the morning and farther than at night. On June 22nd and 5th, the distance between the sun and the earth is equal in the morning and at noon. On August l and February 15, the distance between the sun and the earth is equal at noon and at night. This was calculated in 1954 and can be applied to 100. 100 years later, there will be a difference of one day.

It can be seen that such a complicated problem is too profound for people living in the Spring and Autumn Period. However, this thoughtful and inquisitive quality of the ancients is worth learning. No thinking, no exploration. We believe that no matter how difficult the exploration is and how complicated the calculation is, as long as we work hard from generation to generation, we will be able to uncover many secrets of nature and calculate the change of the distance between the sun and the earth, which is the result of the efforts of generations.