The second is the existence of Huang Chijiao.
How do the four seasons change? It is related to revolution, but the decisive condition is that the earth must turn around the sun obliquely; If the earth rotates vertically around the sun, the sun's rays will always be directly near the equator of the earth, and the angle between the ground plane and the sun's rays from other places will never change, so the four seasons on the earth will not change.
We know that the temperature of a plane on the earth is related to whether the sunlight is direct or oblique to the plane. So how did this effect come about? Let's analyze it. Suppose there is a beam of fixed size. When it is directly incident on a plane, the spot it projects on the plane will be a perfect circle, while when it is inclined, the spot will be an ellipse. The more inclined the ellipse is, the more light it will shine on a larger area. We can understand that the light in the spot area is thinner when the beam is inclined and thicker when the beam is direct. This is why the temperature is higher in direct sunlight and lower in oblique sunlight. We know that temperature is the main factor that determines the season, so it is not difficult for us to understand that the direct sunlight will be in summer, the most oblique light will be in winter, and the place in between will be in spring or autumn.
So how is the alternation of the four seasons formed? This is related to the tilt of the earth. It is precisely because the earth rotates around the sun obliquely, and the direct sunlight sweeps across the north and south once a year with the equator as the center and the tropic of cancer as the boundary, thus forming a phenomenon that the seasons on the earth alternate and orderly all year round.
The specific situation is as follows: when the earth revolves around March 2 1, the sun shines directly at the equator. At this time, the sun in the northern hemisphere is oblique, it is spring, and it is autumn in the southern hemisphere. When the earth turns to the position around June 22, the sun shines directly on the Tropic of Cancer, and the northern hemisphere enters summer, while the southern hemisphere is winter. Around September 23, the sun shone directly on the equator again, and the northern hemisphere entered autumn and the southern hemisphere turned into spring. When the earth turns to the position around 65438+February 22, the sun shines directly on the tropic of Capricorn, and the northern hemisphere enters winter and the southern hemisphere enters summer. Next, we will enter a new year, and a new round of four seasons will begin again.