Polar night begins when the sun stays below the horizon for an entire 24-hour cycle and does not rise again for days, weeks, or months. It happens exclusively in the polar regions, roughly above 66.5° North latitude and below 66.5° South latitude, and its timing depends on which hemisphere you are in. In the Arctic, polar night falls during the Northern Hemisphere winter, roughly from late November through late January at most inhabited locations. In Antarctica, it mirrors the opposite season, spanning roughly May through July. But the phenomenon is far more varied than the simple image of months of total blackness, and its effects ripple through everything from ocean ecosystems to human sleep patterns.
Where Polar Night Occurs and How Long It Lasts
The key geographic requirement is simple: you need to be poleward of the Arctic Circle (about 66.5°N) or the Antarctic Circle (about 66.5°S). The closer to the pole you go, the longer the sun stays away. Duration increases by roughly six days for each additional degree of latitude. At around 68°N, polar night lasts about one month. At 78°N, the latitude of Svalbard, it stretches to about three and a half months. At 88°N, the sun is gone for roughly five and a half months, and at the North Pole itself, polar night lasts close to six months.
1Springer Link. Light in the Polar NightThe same pattern holds in the Southern Hemisphere, though fewer people experience it firsthand because there are no permanent civilian settlements deep in Antarctica. Research stations like Concordia (Dome C) at roughly 75°S and the Amundsen-Scott South Pole Station at 90°S endure months of darkness. In contrast, the Arctic has towns and cities well within the polar night zone. Tromsø, Norway, at about 69.4°N, is the largest city that regularly goes through polar night. Murmansk in Russia, Longyearbyen on Svalbard, and communities across northern Canada, Alaska, Greenland, and Iceland’s Grímsey island all experience it to varying degrees.
Because Earth’s axial tilt drives the phenomenon, polar night is locked to the winter solstice in each hemisphere. In the Arctic, the December solstice marks the midpoint of polar night. In Antarctica, the June solstice does. The dates when polar night begins and ends shift depending on exact latitude. At Tromsø, the sun dips below the horizon around November 21 and returns around January 21. At Svalbard’s Longyearbyen, the window is wider: roughly late October to mid-February.
Not All Polar Night Is Pitch Black
One of the biggest misconceptions about polar night is that it means total, unbroken darkness for months. In reality, most places that experience polar night still get hours of twilight each day, and the quality of that twilight varies enormously. Researchers distinguish several grades of polar night based on how far below the horizon the sun sits.
When the sun is just barely below the horizon (between 0° and about −6°), civil twilight still illuminates the sky enough to see clearly outdoors without artificial light. This is the mildest form of polar night and what most Arctic cities actually experience for most of the period. There is a soft, blue glow around midday that can feel like an extended dawn or dusk. At higher latitudes, the sun drops further, and the sky enters nautical twilight (−6° to −12°), where the horizon is still faintly visible but artificial light is needed for most tasks. Beyond that comes astronomical twilight (−12° to −18°), where the sky is dark enough for full stargazing but a faint residual glow from the sun may still affect the upper atmosphere.
True astronomical polar night, where the sun is more than 18° below the horizon and the sky is as dark as it gets, only occurs at very high latitudes. Even at Longyearbyen (78°N), astronomical polar night lasts only a few weeks in late December and early January. At Tromsø, the sun never drops far enough below the horizon for astronomical polar night at all. The overall darkness is real, but for most communities it is more of a prolonged blue twilight than absolute blackness.
How Polar Night Affects Sleep and Mood
Living without sunrise for weeks or months puts real pressure on human biology. Your circadian clock relies heavily on light cues to stay synchronized with a 24-hour day. During polar night, those cues weaken or vanish, and the body starts to drift. Research on people living in polar regions has found that the circadian system frequently delays during winter, meaning internal rhythms shift later relative to the clock. In a few individuals, the internal clock detaches from the 24-hour schedule entirely and begins running on its own natural period, which is usually slightly longer than 24 hours.
2PubMed Central. Biological rhythms during residence in polar regionsSleep problems are one of the most consistent findings. A large population study in Tromsø, conducted at 69.4°N, compared people who filled out questionnaires during the polar night with those surveyed in summer. The odds of reporting sleeplessness during polar night were over 50% higher than in summer, and the odds of broader sleeping problems were about 80% higher.
3PubMed Central. Is there a negative impact of winter on mental distress and sleeping problems in the subarctic: The Tromsø StudyWhat surprised researchers in that same Tromsø study was the mental health picture. Despite the sleep disruption, there was no significant seasonal difference in reported mental distress. About 7.4% of respondents overall scored above the threshold for high mental distress, but that rate did not climb during polar night compared to summer.
3PubMed Central. Is there a negative impact of winter on mental distress and sleeping problems in the subarctic: The Tromsø StudyBroader reviews of polar health have reached a similar conclusion: true seasonal affective disorder appears to be relatively rare among polar residents, though milder, subsyndromal versions are reported.
2PubMed Central. Biological rhythms during residence in polar regionsThe gap between poor sleep and stable mood may reflect cultural adaptation. Communities that have lived with polar night for generations tend to have well-established coping strategies: bright indoor lighting, strong social routines, and community events concentrated in the darkest weeks. Many residents of northern Norway describe the period as cozy rather than oppressive, though newcomers and researchers on temporary Antarctic postings often find it harder to adjust.
Life in the Dark Ocean
For decades, marine biologists assumed that Arctic ocean life essentially shut down during polar night. No sunlight means no photosynthesis, which means no phytoplankton bloom, and without that base of the food web, everything higher up should go quiet. That assumption turned out to be wrong.
One of the clearest signs of continued activity is diel vertical migration, the daily up-and-down movement of zooplankton and small fish through the water column. In sunlit seasons, these organisms rise toward the surface at night to feed and sink during the day to avoid predators. Acoustic monitoring in Kongsfjorden, Svalbard, showed that this vertical migration continues right through the polar night. Even more striking, around the full moon in December and January the rhythm shifted from a roughly 24-hour solar cycle to a roughly 25-hour lunar cycle. Moonlight, faint as it is, was bright enough to trigger the same avoidance response that sunlight normally produces.
4PubMed Central. Diel vertical migration of Arctic zooplankton during the polar nightAt the genetic level, organisms are keeping internal clocks ticking even without a sunrise. The Arctic scallop, a cold-water shellfish common in the region, shows oscillating expression of clock genes in multiple tissues throughout the polar night. Some of those oscillations shifted from a daily rhythm to a tidal rhythm as the season changed from equinox to polar night, suggesting the animals were switching their timekeeping cue from light to the tides.
5PubMed Central. Rhythms during the polar night: evidence of clock-gene oscillations in the Arctic scallop Chlamys islandicaThese findings have reshaped how scientists think about polar ecosystems. Rather than a dead season, the polar night is a period of lower but real biological activity, sustained by residual light, moonlight, bioluminescence, and internal biological rhythms that organisms maintain even when external light cues all but disappear.
Artificial Light as a New Ecological Force
Against that backdrop of life adapted to extreme darkness, human-generated light is emerging as a significant disruptor. Research vessels, coastal towns, oil platforms, and shipping traffic all introduce artificial light into an environment that evolved under some of the lowest natural light levels on Earth.
Ship-based studies have found that turning on a vessel’s lights during the polar night can cause an almost immediate response in marine life. Fish and zooplankton reacted within five seconds, and the effect extended throughout the water column down to at least 200 meters, well into the mesopelagic zone. Animals changed both their vertical position and their swimming behavior. The finding raises a practical problem for fisheries science: acoustic stock surveys conducted from illuminated ships during the dark season are likely biased, because the very act of measuring the fish drives them away.
6Communications Biology. Artificial light during the polar night disrupts Arctic fish and zooplankton behaviour down to 200 m depthSeabirds respond too, though not uniformly. Citizen-science observations paired with satellite measurements of artificial light around Longyearbyen found that overall seabird diversity decreased as light intensity rose. But individual species told different stories. The Black Guillemot, a fish-eating species dominant in the area during polar night, actually showed an increased presence under brighter artificial light, possibly because lit waters attract the small fish it feeds on. The Little Auk, which eats zooplankton, showed the opposite pattern, declining where light was brightest.
7Remote Sensing in Ecology and Conservation. Illuminating the Arctic: Unveiling seabird responses to artificial light during polar darkness through citizen science and remote sensingThese species-level differences make the problem tricky to manage. Blanket restrictions on artificial light might help zooplankton-feeding seabirds but reduce foraging opportunities for fish-eating ones. As Arctic shipping and resource development increase, understanding these trade-offs becomes more urgent.
What Happens in the Atmosphere
The polar night creates atmospheric conditions found almost nowhere else on Earth. Without incoming solar radiation for months, the surface radiates heat away continuously. Over the high Antarctic plateau, this produces intense surface-based temperature inversions, where the air near the ground becomes dramatically colder than the air just a few hundred meters above it. Researchers at the Concordia station on Dome C, one of the coldest spots on the planet, have documented sudden regime transitions in the strength of these inversions during the polar winter, where the inversion can rapidly strengthen or collapse.
8PubMed Central. Transitions in the wintertime near-surface temperature inversion at Dome C, AntarcticaHigher in the atmosphere, the polar night plays a direct role in one of the most consequential atmospheric chemistry problems of the past half-century. Polar stratospheric clouds form in the extremely cold conditions of the polar winter stratosphere. These clouds provide surfaces where inactive chlorine and bromine compounds are converted into reactive forms that destroy ozone once sunlight returns in spring. The clouds themselves require the sustained cold of the polar night to form and persist. This is why the ozone hole appears over Antarctica in September and October, just as spring sunlight hits a stratosphere that has been primed with reactive chemicals throughout the long winter darkness.
9Copernicus Publications. Mountain-wave induced polar stratospheric clouds and their representation in the global chemistry model ICON-ARTIn the Arctic, the same chemistry occurs but typically produces less severe ozone depletion, because the Arctic stratosphere does not get as cold or stay as stable as its Antarctic counterpart. The polar vortex over the North Pole is more frequently disrupted by weather systems propagating up from lower latitudes. Still, in unusually cold Arctic winters, significant ozone losses have been recorded, and climate models suggest that a changing atmosphere could make those events more common.
Polar Night on Mars
Earth is not the only planet with polar night. Any world with axial tilt experiences it. Mars, tilted at about 25°, has polar nights of comparable relative duration to Earth’s, and they matter enormously for how the planet’s atmosphere behaves.
During the Martian southern polar night, temperatures can fall low enough for carbon dioxide, the main atmospheric gas, to condense directly out of the air and onto the surface as dry ice. Researchers using data from Mars orbiters have studied supersaturation in the southern polar night, where atmospheric temperatures drop below the point at which CO₂ should theoretically condense. This supersaturation process does not just frost over the poles. It affects the planet’s global atmospheric dynamics, because substantial amounts of the atmosphere are literally freezing out at one pole while sublimating at the other, driving pressure differences and large-scale wind patterns that shape the whole Martian climate.
10Journal of Geophysical Research: Planets. A Study on CO2 Supersaturation in the Martian Southern Polar Night Using Mars Global Surveyor Radio Occultation Profiles Rederived With Mars Climate Sounder Temperature ClimatologyThe contrast with Earth is instructive. On our planet, polar night drives water-ice formation in clouds and on the surface, and the seasonal transfer of energy between sunlit and dark hemispheres influences weather patterns thousands of kilometers from the poles. On Mars, the same geometric phenomenon freezes and unfreezes the atmosphere itself. The underlying driver, axial tilt producing a hemisphere cut off from solar energy for months, is identical. The consequences differ because of what each planet’s atmosphere is made of.
Practical Tips for Visiting During Polar Night
If you are planning to experience polar night firsthand, the most accessible places are in northern Norway and Svalbard. Tromsø is easy to reach by air and offers full urban amenities during its polar night season, roughly late November to late January. Longyearbyen on Svalbard has a longer, deeper polar night starting in late October, but its small-town infrastructure limits options. Northern Finland (Utsjoki, Nuorgam) and northern Sweden (Kiruna, though just barely) offer alternatives.
A few things catch visitors off guard. First, your body clock will fight you. Bright-light exposure from a light therapy lamp in the morning can help anchor your sleep cycle. Locals in Tromsø often keep their homes brightly lit and maintain consistent wake-up times regardless of the darkness outside. Second, “dark” does not mean you cannot see. During the midday twilight hours, you may get enough ambient light for photography, short hikes, or simply watching the blue horizon. If the moon is up and there is snow cover, the landscape can feel surprisingly well-lit. Third, polar night is prime aurora season. The long darkness and the location of the auroral oval make the weeks around the winter solstice some of the best times anywhere on Earth to see the northern lights, and you do not even have to stay up late to catch them.
For those headed to Antarctic research stations, the experience is more extreme. Concordia and the South Pole Station are higher in latitude and elevation, with temperatures that can drop below −70°C. Station personnel typically prepare months in advance, and winter-over crews are screened for psychological resilience. The darkness there is deeper, the isolation more total, and the temperature inversions create bizarre optical effects where distant objects can appear to float above the horizon.