All life on Earth directly depends on the Sun. Even deep-sea fish, blind from birth and perfectly dispensed with light, cannot survive without the warmth that our star delivers on the planet. Neither plants, nor bacteria, nor highly organized organisms can exist without the energy that the Sun provides.
Uneven heating and lighting: the first reason
However, light and heat do not reach the Earth’s surface in equal numbers. There are several reasons for this. First of all, the planet has an almost spherical shape (albeit slightly flattened from the poles). Accordingly, the rays of our sun reach the earth's surface at different angles. Where the angle of incidence is closer to the straight line, the Earth heats up and illuminates more. Where the sun's rays touch the planet in passing, it is much cooler.
Uneven heating and lighting: factor two
The second reason is that our “ball” does not move vertically in the orbit, its axis has some inclination towards the ecliptic. This angle of inclination causes the heating and lighting to become uneven. If the axis were perpendicular to the plane along which the Earth circles around the Sun, day and night would be the same duration, and the time of year would always be the same.
These factors determine the existence of certain zones, which are called "Earth's light belts."
Hot belt
Depending on the magnitude of the angle of incidence of the rays on the Earth, there are the climate, the length of the night-day, the average annual temperature, and, accordingly, the “set” of plants and animals that live in a certain area. So how many light belts on Earth? They are distinguished by three main ones, but two of them (hot and polar) are divided into two more (northern and southern). So if you observe this unit, then the question of how many lighting belts will be correctly answered is five.
The hottest is tropical. If we consider the belt of Earth's illumination in percentage terms, then the hot will take forty percent of the entire surface. It is characterized by the warmest climate, although the change of seasons occurs, but there are no sharp differences, say, between winter and summer, day and night in duration are almost the same. The sun during the year in the zone of this belt of illumination of the Earth twice occurs at its zenith (March 21 and September 23, when we have the spring and autumn equinoxes, respectively ), and the rest of the time it rises high above the horizon.
If we recall the hypothetical assumption about the vertical axis of the planet to the ecliptic, then with respect to the tropics, little would change, because even under the existing conditions, the sun's rays fall here almost vertically.
Temperate zone
It occupies more than half of our planet, if you observe the utmost accuracy, then 52 percent. A feature of this belt of Earth illumination is a clear change of seasons in most of the territory it occupies. The length of the night and day in these latitudes depends on the time of the year: in winter, the dark time of the day is longer, in the summer - daytime.
Closer to the polar circles, a phenomenon called white nights is traced, when the luminary hides very briefly behind the horizon, due to which the evening dawn smoothly passes into the morning. On such nights it does not happen dark, and at midnight it can be seen almost like during the day.
For the temperate belt of the Earth's illumination, it is also characteristic that the Sun in it never reaches its zenith.
The change of seasons determines the difference between vegetation and tropical. If the latter is green all year round, here most of the bushes and trees “fall asleep” during the cold months, that is, it discards foliage and stops growing. Some species of animals also hibernate for the winter, which does not happen in a hot belt.
December 22 and the same number in June are significant in that the day and night on these dates are the longest. So, on December 22, the night takes a longer time of the day, and on the following days it is gradually decreasing. And on June 22, the day is longer than night; but then it shrinks, preparing nature for winter sleep. From an astronomical point of view, they are also interesting on March 21 and September 23, when day and night are equal.
Cold belts
These are the smallest zones of all. They occupy only eight percent of the planet Earth. In another way, they are also called polar, which very accurately describes their location: these zones of the Earth's illumination on the map coincide with the North and South poles.
Winter and summer here practically coincide with night and day: in the winter months the Sun is generally absent in the sky, in the summer months it does not leave it. In addition, it should be noted that the summer here is very short, and the star, although it does not hide behind the horizon, practically does not heat the earth. Its rays almost do not touch the surface - their angle of incidence is too acute. We can say that the white nights observed in the temperate zone are the threshold of the polar days and nights.
Cold and low light determined the scarcity of flora in the polar zones. The closer to the center of the belt, the less vegetation. If in the circumpolar circles there is at least moss, then even he does not survive at the poles. The same goes for animals. The farther from the pole, the greater the diversity.
In general, it is easy to see that the Earth's light belts have a very strong effect on the habitat of all living things on the planet.