The phenomenon of perpetual darkness, where the sun remains below the horizon for more than 24 hours, is known as Polar Night. This extended period of twilight or darkness is a consequence of the planet’s astronomical geometry and affects all locations inside the Arctic and Antarctic Circles during their respective winter seasons. This regular seasonal cycle profoundly shapes the environment and the lives of those who inhabit these high latitudes.
The Science Behind Perpetual Darkness
The existence of Polar Night is a direct result of the Earth’s axial tilt, which is approximately 23.5 degrees relative to its orbital plane around the Sun. This tilt causes the distribution of solar radiation to shift dramatically over the course of the year, leading to the planet’s seasons. During the winter in either the Northern or Southern Hemisphere, that pole is angled away from the Sun, preventing direct sunlight from reaching regions at the highest latitudes.
The boundary where this phenomenon begins is the Arctic or Antarctic Circle, located at about 66.5 degrees North and South latitude, respectively. Any location beyond these circles will experience at least one day when the sun does not fully rise above the horizon. The further a location is from this boundary, the deeper the angle of the sun below the horizon becomes, resulting in a longer period of darkness.
Geographical Locations Experiencing Polar Night
These regions of extended darkness are found in the northernmost parts of countries, as well as the continent of Antarctica. In the Northern Hemisphere, Polar Night occurs in areas of Norway, Sweden, Finland, Russia, Greenland, Canada, and the United States, specifically Alaska. The duration of the sunless period in a specific settlement is entirely dependent on its latitude, with locations closer to the pole experiencing a longer dark season.
Utqiagvik, Alaska, is the northernmost city in the United States and experiences a Polar Night that lasts for around 65 days, typically from mid-November to late January. The Norwegian archipelago of Svalbard is home to the town of Longyearbyen, which endures about two and a half months of sunless days. Russia holds the largest area of territory that experiences the phenomenon, with regions like Dikson in the Krasnoyarsk Krai experiencing nearly three months of darkness.
Duration and Types of Polar Night
The term “Polar Night” does not always mean pitch-black darkness, as the intensity of the darkness varies greatly depending on the sun’s angle below the horizon. The length of the Polar Night ranges from a single day just inside the Arctic Circle to nearly six months at the geographic poles. For every degree of latitude one moves past the Arctic Circle, the duration of the Polar Night increases by approximately six days.
This variation in light is categorized by three distinct types of twilight. Civil Twilight occurs when the sun is between zero and six degrees below the horizon, providing enough scattered light for outdoor activities without artificial aid. Nautical Twilight follows, with the sun six to twelve degrees below the horizon, making the horizon indistinguishable and requiring artificial light for most tasks. Astronomical Twilight, where the sun is twelve to eighteen degrees below the horizon, is virtually indistinguishable from a true night sky, as very little sunlight is scattered by the atmosphere.
Life in the Continuous Dark
Human and animal life in these regions has developed biological and cultural methods to manage the long period of darkness. Biologically, the lack of sunlight presents challenges like Vitamin D deficiency, as the body cannot synthesize the vitamin without ultraviolet light exposure. The disruption of the natural light-dark cycle can impact the body’s internal clock, or circadian rhythm, and contribute to Seasonal Affective Disorder (SAD) in some residents.
To counteract these effects, communities rely heavily on artificial light, with residents using specialized light therapy lamps that mimic the spectrum and intensity of daylight. Culturally, residents embrace the dark season with festivals and a focus on indoor, community activities during the “blue hour” of twilight around midday. Animals also exhibit adaptations, such as reindeer, whose eyes change structure to increase their sensitivity to light, allowing them to see in the ultraviolet spectrum and better locate food in the snow.