The earth is in the constant movement: rotates round its pivot-center and orbits around the Sun. There is a change of day and night. There are a summer and winter, spring and fall. All living beings on the planet live according to this rhythm established by the nature.
Instruction
1. Every day, rising on the horizon from East side, the Sun passes across the sky and is behind the horizon in the West. In the northern hemisphere it occurs from left to right. Inhabitants of the southern hemisphere see this movement from right to left. The whole revolution of Earth is made round its pivot-center in 24 hours. This rotation causes change of day and night.
2. If 24 hours to divide equally — it turns out that 12 hours last day and 12 hours — night. On the equator honor it and occurs. But inhabitants of middle latitudes noticed that it not so. In the summer day lasts long, and in the winter it is absolutely small. Why then in the summer so long day?
3. The thing is that the Terrestrial axis is inclined concerning the plane of the orbit. The code a northern part of an axis is inclined to the Sun, then in the northern hemisphere summer. The sun at noon is highly over the horizon and it needs more time to pass a way from the East on the West. Thus day lasts more than 12 hours (in middle latitudes of both hemispheres, it is about 17 hours). But day remains always identical duration; therefore, all rest of the time (7 hours) stays overnight.
4. But there is such interesting fact: being in the middle of summer on the North Pole, the Sun moves over the horizon day and night. And then gradually its daily course bends and time when the Sun begins to hide for a short time behind the line of the horizon comes. And the closer to winter, the longer the Sun does not appear. And in the winter it is not in the sky at all. On the North Pole there came polar night. But how so it turns out that the axis itself bends to the Sun, from it?
5. The axis does not deviate in itself, it is inclined constantly in one direction. Earth appears on the one side of the Sun, with another, passing around it on the orbit in 365 days. Thus, northern and southern poles serially appear on sunny side.
6. On the equator at noon, the Sun is slightly inclined to the horizon. In the middle of the spring and in the middle of the fall the Sun at noon is in a zenith, i.e. directly over the head. At this time upright objects do not cast a shadow. In the middle of the summer the Sun is in a zenith over the width called the Tropic of Cancer. It is width 23 °. In the middle of the winter, on the contrary — the Sun is in a zenith at the same width over the southern tropic. It is called the Tropic of Capricorn (it is in this constellation at this time).
7. Thus, because of an inclination of an axis and the address of Earth on an orbit around the star, seasons and duration of light day change. There are also some deviations in rotation of Earth round its pivot-center. The axis itself kind of rotates concerning the center (it is also the center of the globe). The full cycle of such rotation of an axis occurs for 25 thousand years and is called Platonic year.