The polar day (or Antarctic polar night) in the Arctic begins at the vernal equinox (about 2 1 March) and ends at the autumnal equinox (about 23 September), lasting about 186 days. The polar night in the Arctic (or the polar day in the Antarctic) begins at the autumnal equinox and ends at the vernal equinox, and lasts about 179 days. The maximum dividing line between polar day and polar night is on the latitude line of 66 34'. Extreme day and night are strange natural phenomena that can only be seen in the south and the Arctic Circle. When there is extreme sunlight, the sun always hangs in the sky within 24 hours a day; When it is extremely dark, there is no trace of the sun for 24 hours a day, and it is dark all around. This phenomenon occurs because the earth's orbit around the sun is an ellipse, and the sun is at the focus of this ellipse. Because the earth always revolves around the sun horizontally, that is, there is an included angle of 66 33' between the rotation axis of the earth and the revolution plane, and this included angle is constant during the operation of the earth. Therefore, the direct sunlight point on the earth is not fixed, but moves from north to south. At the vernal equinox and autumnal equinox of a year, the sun shines directly on the equator, and at this time, the length of day and night is equal everywhere on the earth. After the vernal equinox, the point of direct sunlight gradually moved northward, when the polar day and the polar night appeared in the North Pole and the South Pole respectively. Until the summer solstice, the sun shines directly on the Tropic of Cancer, and the extreme sun phenomenon can be seen throughout the Arctic Circle; The extreme night phenomenon can be seen throughout the Antarctic circle. On the solstice of winter, the sun shines directly on the tropic of Capricorn. At this time, the whole Antarctic circle can see the extreme day phenomenon, and the whole Arctic circle can see the extreme night phenomenon. Source: Middle School Political History Geography Teaching Guidance Edition