Polar night is a period of continuous darkness lasting six months in the polar regions due to the Earth’s tilted axis. The lowest temperatures on Earth have been recorded during this time, and some settlements experience long periods of darkness, which can lead to depression. The inverse is polar day, where there is an extended day during the summer. Some areas experience polar twilight, and other planets like Pluto have similar phenomena.
Polar night refers to nights longer than 24 hours that occur seasonally in the polar regions of the Earth. Since the Earth’s axis is tilted 26 degrees from the plane of the elliptical, there are parts of the poles whose rotational path is never exposed to light. The north and south poles are the darkest areas of all, each receiving six months of continuous night and six months of continuous day. The depth of polar night in the polar regions is when the lowest temperatures on Earth have been recorded, 89 degrees Celsius below zero, or negative 128 degrees Fahrenheit, measured at Vostok Station, Antarctica. Without heavy furs, this can lead to death in less than two minutes.
The formal definition of the Arctic and Antarctic Circle has to do with the polar night. Inside the circle, there is at least one 24-hour period of complete darkness during the year, while outside it, darkness lasts less than 24 hours. Some settlements in the far north and far south have very long nights, with only a few hours of sunshine during the day during the winter. Examples include Hammerfest, Norway and research stations across much of Antarctica. Being deprived of light up to this point can be a risk factor for depression.
The inverse of polar night is called the midnight sun, or polar day, where there is an extended day during the summer. This can make the environment (relatively) warm and allow long walks on the ice, like the one made by Roald Amundsen, the Norwegian polar explorer who was the first to reach the South Pole in 1911. Without a night to tell, the travelers they can leave when they want and have no freezing darkness in which to suffer.
In some areas, instead of polar night, there is instead polar twilight, where the sun dips below the horizon, but by less than 10 degrees, bathing the entire landscape in a surreal and expansive twilight. This light is enough for people to walk the streets and work, and some cities in the Far North live with this twilight for months.
Some other planets, such as Pluto, have such great axial tilt that large percentages of their surfaces experience polar day and night. In the case of Pluto, this can lead to temperatures as low as 33 degrees Celsius above absolute zero.
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