It is not easy to imagine that daylight hours last more than 24 hours, that it does not change at night, and it is always light outside. Or, on the contrary, all the time night, darkness, cold. But so it is beyond the inner borders of the polar circles.
A polar day is a period during which the sun is above the horizon and does not set behind it for more than one day. Such a phenomenon can be observed in the polar regions located north of the Arctic Circle and south of the Arctic Circle.
A polar day is possible due to the inclination of the Earth's equator plane with respect to the ecliptic plane by approximately 23 ° 26 ′. It lasts almost two days at the polar circles and increases the duration at higher latitudes to 186 days at the poles. It is the shortest at a latitude of approximately 65 ° 43 ′. The longest - at the North and South poles. There, its duration reaches six months. At the North Pole, it begins on March 17 and lasts until September 25. And at the South Pole it lasts from about September 20 to March 22. During the polar day, the sun does not set every day beyond the horizon, but makes a circle parallel to the horizon. In addition, the phenomenon of refraction allows you to observe the presence of the sun simultaneously at both poles for several days in a row before and after the equinoxes.
Near the outer side of the polar circles, polar night is observed. During this period, the sun has not been in the sky for more than a day. The boundary of a constant night near the Arctic Circle is approximately latitude 73 ° 5 'to the South. Such a night can last a maximum of 178 days.
The beginning and duration of the polar days and nights are different for different settlements. They also have different weather conditions. This is due to their location at a certain geographical latitude. For example, in the north, in Zapolyarny, the polar night lasts from November 30 to January 13; in Murmansk begins on December 2, and ends on January 11; The Polar Dawns (the weather in which is very severe in winter) meet her on December 21, and see off on the 23rd of the same month.
As we have already seen, these phenomena have a duration of approximately 186 - 178 days, that is, at the poles, the day lasts six months, and the night lasts six months. And these periods determine the weather conditions on the ground. There do not exist four seasons of the year, but only conditionally divided summer (on a polar day) and winter (when a polar night comes). But what happens to our planet during such periods?
In summer, one of the poles of the Earth faces the Sun and does not go into shadow, despite the rotation of the planet around its axis. On this site is a polar day. But he is not like we used to see him. After all, it cannot be called part of the day, because it lasts for six months. Since the pole is directed towards the luminary, then, accordingly, the Sun does not hide behind the horizon, but moves along it.
At the opposite pole, a completely different situation is observed. Since at this time he has been in the shade for almost half a year, a constant night continues on it. The sun does not appear above the horizon.
Shortly before the polar day, a fascinating natural phenomenon - the northern lights - appears on the "gloomy" pole. When it arises, it becomes lighter around, as with a full moon. Aurora borealis is just an optical effect, but what a spectacular one! How many people dream of seeing him live at least once!
Aurora borealis occurs in the upper atmosphere due to the interaction of the Earth's magnetic field with cosmic particles. This is the glow of air at an altitude of 60 to 1000 km in the form of arched rays, curtains, crowns. It can be seen at the poles of both hemispheres, but with different intensities, depending on longitude. It lasts from several minutes to several days and can appear at different times of the year only in the night sky.