What is the mystery of extreme day and night?

The mysterious South Pole and North Pole are always elusive. There are too many anecdotes here, among which the extreme day and night are one. As the name implies, the extreme day is 24 hours a day, and vice versa. When there is an "extreme day", the sun is always near the horizon of the South Pole or the North Pole. In "Extreme Night", the sky is not as dark as we thought, but it is particularly bright under the irradiation of moonlight and starlight.

The cause of extreme day and night

As we all know, during the earth's revolution, the earth's axis always points in the direction of Polaris, and the earth's axis always keeps a certain angle with the revolution orbit. The revolution of the earth makes the direct point of the sun on the surface of the earth always change. Between the vernal equinox and the autumnal equinox, the sun always shines on the low altitude of the North Pole. At this time, the North Pole is full of daytime, with "extreme daytime". However, after the autumnal equinox and before the vernal equinox next year, the direct point of the sun moved to the southern hemisphere and stayed up all night in the Arctic, resulting in "extreme night". The polar days and nights in Antarctica are just the opposite of those in the North Pole.

The reason for the darkness before dawn

The darkness before dawn is the darkest, which is the result of the interaction between the earth's atmosphere and sunlight. At the end of the long night and dawn, the sun below the horizon shines on the upper atmosphere of the earth 2000 ~ 3000 kilometers. In this way, the light of the stars is diluted by the scattered light of the sun, and the upper atmosphere is so thin that the scattered sunlight cannot be completely transmitted to the ground. At this moment, there is neither starlight nor scattered light from the atmosphere on the earth, which is the darkest time of the day.