Why are we having summer when the earth is far from the sun?

Every moment, the Earth is revolving around the Sun. Since the Earth has an elliptical orbit, the distance between the Earth and the Sun is not constant in the process of revolving around the Sun, sometimes the Earth is far away from the Sun, and sometimes it is closer to the Sun.

For us living on the Earth, the Earth every revolution, we have spent a year, but also experienced a cycle of the seasons, according to common sense, the temperature on the Earth should be closer to the sun the hotter, the farther the colder, so a reasonable guess is that when the hot summer comes, the Earth should be closer to the sun is right.

But this does not seem to be the case, because the Earth will run to the aphelion in early July every year, when we are having summer, so the question arises, why are we having summer when the Earth is far away from the sun? Isn't it supposed to get colder as it gets farther away? Let's talk about this topic.

According to the inverse square law, the radiation intensity of the sun is inversely proportional to the square of the distance. It is known that the distance between the perihelion point of the Earth's orbit and the sun is about 152 million kilometers, and the distance between the aphelion point and the sun is about 147 million kilometers. A simple calculation shows that the difference between the solar energy that the Earth's surface can receive per unit area at the aphelion point and the aphelion point is about 6.4%.

From this point of view, the Earth's temperature should indeed be lower when the Earth is far from the sun, however, there is another important factor that affects the temperature of the Earth, that is, the angle of incidence of sunlight on the Earth's surface, to illustrate this point, we can take a common flashlight to give an example.

If we turn on a flashlight, and then let the light from the flashlight shine on the wall, then the wall will appear as a spot of light, at this time we can change the area and brightness of this spot by adjusting the angle of incidence of light on the wall.

A simple experiment can know that when the light is perpendicular to the wall, the area of the spot is the smallest, and its brightness is also the highest, and with the increase in the tilt of the light, the area of the spot is larger, the brightness is also lower.

This shows that the light received per unit area of the spot is closely related to the angle of incidence of the light from the flashlight on the wall. The smaller the tilt of the light, the more light is received per unit area of the spot, and the most light is received per unit area of the spot when the light is directed to the wall.

Now let's imagine the sun as an oversize flashlight, then the angle of incidence of sunlight will appear different in different areas of the earth's surface. Why? Because the Earth is a sphere.

By the same token, the direct sunlight area on the Earth's surface receives the most solar energy per unit area and the highest temperature, while in other areas, the greater the tilt of the sunlight, the less solar energy per unit area on the Earth's surface, and its temperature will decrease.

Since the Earth's rotation axis has an axial inclination of about 23°26′ concerning the ecliptic plane (i.e. the plane where the Earth's orbit is located), this causes the direct sunlight area on the Earth's surface to move back and forth in the north-south direction with the Earth's rotation.

The northernmost and southernmost limits of direct sunlight on the Earth's surface are called the "Tropic of Cancer" (about 23°26′N) and the "Tropic of Capricorn" (about 23°26′S), which means that during the year, the sunlight, In this case, the solar energy received per unit area varies for a particular area of the earth's surface.

The degree of this variation varies depending on latitude and can be as high as 50% near the Tropic of Cancer and Tropic of Capricorn, compared to the 6.4% difference between the solar energy received per unit area of the Earth's surface at aphelion and aphelion. In contrast, the difference in solar energy per unit area of the Earth's surface at the aphelion and aphelion is only about 6.4%, which means that what determines the temperature of the Earth's surface is the angle of incidence of sunlight.

For us living in the northern hemisphere, the Earth is far from the sun (that is, located near the aphelion), the direct sunlight area is actually near the "Tropic of Cancer", in this case, the surface of the northern hemisphere per unit area to receive more solar energy, the temperature is higher, so we are living in summer.

After reaching the "Tropic of Cancer", the direct sunlight area will start to move south, and the temperature of the northern hemisphere will gradually drop, when it moves near the equator, we are in the autumn, when it moves near the "Tropic of Cancer", we are When it moves to the equator, we're in the fall, when it moves to the Tropic of Capricorn, we're in the winter, and when the direct sunlight moves north again to the equator, we're in the spring, then the summer, and so on.

Yes, this is the reason why there are four seasons on earth, but it should be noted that for humans living in the southern hemisphere when the direct sunlight is located near the Tropic of Capricorn, it is their summer, which means that the seasons in the southern hemisphere change in the opposite way to the northern hemisphere.

As for the area near the equator on the earth's surface, because the direct sunlight will experience twice a year, and in the direct sunlight area away from the equator, and not too far from the equator, the temperature in the area the equator is higher throughout the year, there are no obvious reasons.

Well, that's all we have for today, welcome to follow us and we'll see you next time.