The Polar Night is a natural phenomenon defined as the period when the sun remains entirely below the horizon for more than 24 continuous hours. This extended darkness occurs exclusively in the Earth’s polar regions, north of the Arctic Circle and south of the Antarctic Circle. Although often associated with the Northern Hemisphere winter, the same event takes place in the Antarctic during its winter season. This annual cycle profoundly impacts the climate, ecosystems, and human communities at these high latitudes.
The Astronomical Cause
The mechanism behind the Polar Night is the constant tilt of the Earth’s axis in relation to its orbital plane around the sun. The planet is tilted by approximately 23.5 degrees, and this angle remains fixed as the Earth revolves. This fixed tilt causes one hemisphere to be angled away from the sun during its winter months. When the Northern Hemisphere is tilted away, the sun’s rays do not reach the North Pole regions, keeping the sun below the horizon. Six months later, the opposite occurs, and the South Pole experiences its period of continuous darkness.
Defining the Duration by Latitude
The duration of the Polar Night depends directly on a location’s distance from the pole. The Arctic and Antarctic Circles, situated at roughly 66.5 degrees latitude, mark the boundary where the sun fails to rise for just one day during the winter solstice. Moving poleward from this line causes the period of darkness to lengthen significantly.
For instance, at 68 degrees north, the Polar Night lasts for approximately one month. The Alaskan town of Utqiagvik (71 degrees north) experiences a polar night extending for about 65 days, typically from mid-November to mid-January. Further north, at 78 degrees latitude, the continuous night stretches to roughly three and a half months.
The maximum duration is reached at the geographic North and South Poles (90 degrees latitude), where the sun remains below the horizon for nearly six months. Due to the Earth’s elliptical orbit, the Polar Night at the North Pole lasts about 179 days, while the South Pole’s is slightly longer, at approximately 186 days.
The Different Levels of Darkness
Although the sun stays below the horizon for months in the far north, the Polar Night is not a uniform block of absolute darkness. The atmosphere scatters sunlight even when the sun is set, creating different stages of twilight that significantly impact the perceived level of light. These stages are categorized based on the sun’s angular distance, or depression, below the horizon.
Civil Twilight
The brightest phase is Civil Twilight, which occurs when the sun is between 0 and 6 degrees below the horizon. During this time, there is enough light for most outdoor activities to be conducted without artificial illumination.
Nautical Twilight
Once the sun drops further, between 6 and 12 degrees below the horizon, the period is called Nautical Twilight. The horizon remains visible during this stage, which was historically important for sailors navigating by the stars.
Astronomical Twilight
The deepest stage of darkness is Astronomical Twilight, defined by the sun being between 12 and 18 degrees below the horizon. This period is dark enough for astronomers to observe the faintest celestial objects without interference from scattered sunlight.
True Polar Night, where the sun is 18 degrees or more below the horizon for the entire day, is limited to latitudes above about 84 degrees north or south. This condition of complete darkness lasts for only about 11 weeks at the poles themselves, meaning that for many high-latitude communities, the Polar Night is actually dominated by a continuous, extended twilight.