From the point of view of science, the night is very interestingphenomenon. After all, it is very different, which is explained by various phenomena. In some latitudes, it can last for a certain period of time in a certain period of time, and in others it can not occur at all. Let's figure out what a night is, what it is and why it happens.
Times of Day
Scientists call the time interval at night, whenwhich, in the case of our planet, the Sun, is the center of the horizon of the celestial body (for us, the Earth). The duration and features of the current of the night depend on the latitude, the inclination of rotation of the earth's axis, the angle between the Sun and this axis. Due to the fact that the plane of the orbit and the axis of rotation are not perpendicular, changes in duration and other features of the night proceed with a yearly periodicity. The duration of the night reaches its maximum of 21 (22 in leap years) in December, then is reduced to a minimum by 21 (22) July and starts to increase again.
At the moment of crossing the center of the Sun of heavenlyequator, the duration of the day and night is the same. This phenomenon is called "equinox". It occurs twice a year. In the northern hemisphere, the vernal equinox is celebrated on March 21, and the autumn equinox is on 22 or 23 September. In the southern hemisphere, autumn is called spring, and spring - autumn.
About this phenomenon can also be read in the article When the day is equal to the night.
In latitudes, located above the polar circles,one can observe a phenomenon such as a polar night, when the sun does not appear from the horizon. Depending on the location of the territory, the sun's rays can not fall completely during the day (full polar night) or fall partially, creating twilight.
Before and after the summer solstice, when the dayis the longest in the year, in temperate and high latitudes, a phenomenon such as white nights can be observed. Even in the dead of night, the light still hits the Earth, because of which the entire nighttime period resembles twilight.
About the time of the beginning of the white nights read in the article When the white nights begin.
Details on the sun and its "working mechanisms" you can find out in the article Why the sun shines.