Wiktionary
n. A period of darkness that occurs in winter in polar regions north from the Arctic Circle and south from the Antarctic Circle, and during which the sun stays below the horizon.
Wikipedia
The polar night occurs when the night lasts for more than 24 hours. This occurs only inside the polar circles. The opposite phenomenon, the polar day, or midnight sun, occurs when the Sun stays above the horizon for more than 24 hours. "Night" is understood as the center of the Sun being below a free horizon. Since the atmosphere bends the rays of the Sun, the polar day is longer than the polar night, and the area that is affected by polar night is somewhat smaller than the area of midnight sun. The polar circle is located at a latitude between these two areas, at the latitude of approximately 66.5 degrees. In the most northern city of Sweden, Kiruna, at 67°51'N, the polar night lasts for around 28 twenty-four-hour periods, while the midnight sun lasts around 50 twenty-four-hour periods.
Usage examples of "polar night".
The polar night-sun gleamed dully from the horizon through the small windows in the hallway, creating a copper glow, like some vision of purgatory.
Then the lights themselves were gone, and we saw only the stars and the polar night over the desolate horizon.
The sonie carried them out of the polar night into afternoon light, away from the dark ocean, and across land at a height they could only guess at and at a speed they could only dream of.
As the ridge stabilized and ice stopped falling, Rita was shaken by a vivid vision of Harry crushed beneath a shining white monolith elsewhere in the cruel black-and-white polar night.
I am not as sceptical about old tales and fears as I used to be, and I do not laugh now at the prehuman sculptor's notion that lightning paused meaningfully now and then at each of the brooding crests, and that an unexplained glow shone from one of those terrible pinnacles all through the long polar night.
A hundred yards inland from the shore-rim, in a place where there was some moss and soil, I built myself a semi-subterranean Eskimo-den for the Polar night, the spot surrounded by high walls of basalt, except to the west, where they opened in a cleft to the coast, the ground strewn with slabs and boulders of granite and basalt, in three places the snow red, overgrown with a lichen which at first I took for blood.