User:Ail39/Polar night

Description
The length of polar night varies by latitude, from 24 hours just inside the polar circles to 179 days at the poles. As mentioned, a location experiencing polar night does not mean that the location will be in full darkness; in many cases, due to sunlight being refracted over the horizon, a location experiencing polar night may be in one of the various phases of polar twilight. As in locations experiencing daytime, the middle of the day will typically be the brightest time in locations experiencing polar twilight.

For example, a typical day during polar night in Vadsø, Norway will begin with astronomical night, astronomical twilight, nautical twilight, and civil twilight in that order (with each successive phase including more light than the last). Following civil twilight, the day will progress through the other phases in the opposite order (nautical twilight, then astronomical twilight, then astronomical night to end the day).

Effects of Polar Night on Sleep and Mental Health
Numerous analyses have been conducted to examine the effects of polar night on humans. In Tromsø, Norway, a city located at 69 degrees north, there is a 2 month long polar night, lasting from mid-November to mid-January. An analysis was conducted based on 2015-16 data from a health survey that involved residents of the region over age 40, with the goal being to analyze the seasonal variation of sleeping patterns in Tromsø. The study found that there was a higher prevalence of insomnia among men in the fall and winter months, but not among women. However, overall, sleep duration varied little to none throughout the year despite the extreme changes in daylight; it is worthwhile to note that a factor in this result may be the significant amount of artificial light in Tromsø.

A similar study was conducted among men who overwintered at Belgrano II, an Argentine research station in Antarctica. The station is located at 77 degrees south, resulting in a polar night 4 months in length. The study was conducted across 5 different winter campaigns in the 2010s, bringing in a total of 82 participants. The study found that participants generally slept for longer periods of time in the summer months than the winter months. Additionally, greater amounts of social jetlag were observed in the winter months.

A third study aimed to examine the mental health of 88 Korean crew members at two different research stations in Antarctica, King Sejong Station and Jang Bogo Station. No crew members had been diagnosed with a mental illness prior to the study. While in Antarctica, 7 of the 88 crew members were diagnosed with a mental illness during early winter. The mental illnesses included insomnia disorder (3 diagnosed), depressive disorder (1 diagnosed), adjustment disorder (2 diagnosed), and alcohol use disorder (1 diagnosed).

Overall, both Antarctic studies showed a lower amount of sleep beginning at the start of winter, while the study from the Korean bases also showed an onset of mental health problems at that time. While the study from Tromsø did not show a similar drop in sleep duration as the Antarctic studies (perhaps due to the high amounts of artificial light), it did show an increased amount of insomnia in men during winter; therefore, the polar night was shown to have sleep and/or mental health effects in all three studies.