Why are there four different kinds of weather in a year?

Let's analyze the movement of the earth first. There are two basic movements of the earth, one is called rotation-the rotation of the earth itself, and the other is called revolution-the rotation around the sun.

Rotate around the earth axis passing through the north and south poles, and the direction is from west to east. The farther away from the poles, the faster the speed. A circle equidistant from the poles is called the equator. The time for the earth to rotate once is one day, which is 24 hours.

The speed of the earth's revolution around the sun is 30 kilometers per second, which takes 365 days and 5: 48: 46. That is, a year, which is called the Tropic of Cancer in astronomy. The earth's orbit around the sun is elliptical, and the long diameter and short diameter are not much different, which can be approximated as a perfect circle. The sun is in a focus of this ellipse, but the focus is not in the center of the ellipse, so the distance between the earth and the sun is sometimes closer and sometimes farther. At the beginning of 1 month, the earth is closest to the sun, which is 147, 100000 km, which is called perihelion. At the beginning of July, the farthest distance of the earth from the sun is 152, 100000 km, which is called apohelion. In fact, when the earth is at perihelion, it is winter in the northern hemisphere and summer in the southern hemisphere, and it is summer in the northern hemisphere and winter in the southern hemisphere when it is at aphelion. This shows that the change of four seasons has nothing to do with perihelion and apohelion.

So how did 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 shines 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.

-The four seasons-

1. The brightest area on the earth is where the sun shines directly, such as the Tropic of Cancer, Tropic of Capricorn and Equator; Oblique areas are dark, especially where the oblique angle is large, and the light is weak, such as the north and south poles.

2. Affected by the revolution of the earth and the inclination of the earth axis, the areas where the earth is exposed to direct sunlight will be different, and the temperature will change accordingly, thus forming four seasons.

When the sun shines directly on the equator, it is hottest near the equator. The farther away from the equator, the greater the sun's oblique angle and the lower the temperature. At this time, the northern hemisphere is a little far from the equator, which is in spring.

The sun will gradually move northward after hitting the equator. 2 1 When crossing the equator on June 6th, 2002, the sun will be in direct contact with the Tropic of Cancer. At this time, it is the hottest near the Tropic of Cancer, and the northern hemisphere is strongly irradiated by the sun, which is summer.

After the sun hits the Tropic of Cancer directly, it moves southward day by day, and when it returns to the equator, it will be autumn in the northern hemisphere.

6. When the sun continues to move south to the Tropic of Capricorn, the sun's oblique angle in the northern hemisphere is the largest, and the sun's strength is weak. This is winter.

7. After the sun shines directly on the Tropic of Capricorn, it moves northward day by day, and then shines directly on the equator, so it goes on and on, and it rotates in spring, summer, autumn and winter.

8. The temperatures in the four seasons are obviously different. Because of the direct sunlight, the seasons in the southern hemisphere and the northern hemisphere are opposite. When the northern hemisphere is summer, the southern hemisphere is winter. When the northern hemisphere is winter, the southern hemisphere is summer.

-Variation of the length of day and night in four seasons-

The revolution of the earth and the inclination of the earth's axis form the change of the length of day and night in the four seasons. ※.

1. The sun shines directly on the Tropic of Cancer, and it is summer in the northern hemisphere, with long days and short nights.

2. The sun shines directly on the Tropic of Capricorn, and it is winter in the northern hemisphere, with short days and long nights.

The day and night situation in the southern hemisphere is just the opposite of that in the northern hemisphere. The northern hemisphere has long days and short nights, while the southern hemisphere has short days and long nights. When the days in the northern hemisphere are short and the nights are long, the days in the southern hemisphere are long.

4. When the sun shines directly on the equator, it is spring or autumn in the northern hemisphere, which is as long as day and night, about the vernal equinox (about March 2 1) and the autumn equinox (about September 2 1); The longest day is the summer solstice (about June 2 1); The shortest day is the winter solstice (about 65438+February 2 1).