At any point on earth there is a time when it is light, and a time when it is dark. This is due primarily to our main luminary - the Sun. It moves across the horizon, changing the level of lighting. Simply put, it is dark at night because the sun goes below the horizon.
An interesting point of view of ancient people
In ancient times, people assumed that this sun was spinning around our planet and hiding behind the horizon. For a long time no one could even imagine that it was our planet that revolves in a vast outer space around a luminary. The same goes for the moon. The sun and moon were given a divine origin: they were worshiped, brought gifts, praised in songs and ceremonies. But the era of science has come, which has proved that everything happens exactly the opposite. Planet Earth is not the center of the universe, but just its tiny component, and why it is dark at night is not connected with any divine manifestations.
What is the rotation of the Earth and what does it affect
There are two simultaneous movements and movements of the planet in space: orbiting around the Sun, as well as around its own axis, like a baby top. That is, at the same time, when the planet flies in outer space, it revolves around itself, and the combination of these factors is the reason why it is dark at night and light at day. Moving in orbit in space, complete with the fact that the Earth’s axis is inclined to this orbit at an angle of about 66 degrees, is the reason for the changing seasons and their “unevenness”.
In different parts of the Earth, depending on the degree of heating by the rays of the star, autumn, winter, spring and summer change at one time. Thus, the middle latitudes most often visit all four seasons, to varying degrees of their intensity (for example, in Italy, summer, like winter, is much warmer than in Moscow). On the Equator, which for the most part is under direct sunlight, close at 90 degrees at noon, the day lasts partly a little longer than 12 hours.
Poles: why is it cold, even though it's half a day there?
At the poles the picture is in a very special way - the sun's rays fall so that they glide and are almost completely reflected from the surface, not stopping and not leaving heat in it, although day and night here last almost half a year each. That is why the north and south poles are the coldest regions of our planet.
Different lengths of day and night
The rotation of the planet around the Sun, the main star for us, sets the change of seasons, as well as the change of day and night. The spherical shape of the planet, the heterogeneity of the surface and the property of light rays to reflect complement and diversify the climate in similar regions. But there are days when the day comes in all latitudes to the polar zone, having the same time distribution between the clear part of the day and the dark - the days of the spring and autumn equinox. At this time, at the equator, any object will give the smallest shadow, because the sun sends its rays at an angle of 90 degrees to its surface.
In principle, with the question why it is dark at night, everything is clear. But what’s interesting is that it’s dark for a long time, and it happens a little. Our northern hemisphere is characterized by a decrease in night duration from March 21 (spring equinox) to September 23 (autumn equinox), and vice versa - long nights are observed in the winter season. In the southern hemisphere, the opposite is true.
But how to explain this to children?
Explaining to children the fact that it is dark at night because the sun does not shine is not entirely true. After all, in fact, the sun always shines. It does not turn on and off by someone’s decision, like a table lamp. But to talk about the position of the Earth in space, the angles of incidence of rays and other clevernesses that can already be understood by schoolchildren, is not necessary. To do this, it is best for parents to be smart and demonstrate clearly how this happens. In order to explain why it is dark at night, you need to familiarize the child with two concepts: what is the Sun and what is planet Earth. To do this is quite simple: draw two balls, one yellow and with rays (actually the Sun), and the other blue with a similar outline of the mainland. Further, without going into complicated terminology, talk about the form, and clearly demonstrate using a model of the solar system. It will be enough a yellow ball and a small globe, and if there is an opportunity, it is better to buy a full-fledged model or do it yourself, and even with the child.
Show that the sun is standing still, and we are spinning, which is why its rays on different parts of the globe do not always fall. Then the child will understand that it is dark at night, because at this time we turn away from him, substitute the back, so to speak, in the sun. For clarity, you can demonstrate this phenomenon in the dark with the help of the same globe and a flashlight acting as the Sun.