For many, the idea of the sun never setting might seem like a fantasy, but “perpetual daylight” or “polar day” makes this a reality in certain parts of the world. This phenomenon involves the sun remaining visible above the horizon for 24 hours or more, creating extended periods of continuous light. It transforms daily life and the environment in unique ways, offering a stark contrast to the typical cycle of day and night experienced across most of the globe.
The Astronomical Cause
The Earth’s axial tilt, about 23.4 degrees, plays a role in creating continuous daylight. As our planet orbits the sun, this tilt means different hemispheres lean towards or away from the sun at various times of the year. During summer in either the Northern or Southern Hemisphere, that pole tilts towards the sun, receiving more direct and prolonged sunlight.
This tilting results in the sun staying above the horizon for extended periods in the polar regions. At the summer solstice, around June 21 in the Northern Hemisphere and December 21 in the Southern Hemisphere, the tilt is at its maximum towards the sun. This alignment ensures that areas closest to the poles remain bathed in sunlight as the Earth rotates, preventing the sun from dipping below the horizon. The Earth’s rotation still occurs every 24 hours, but the angle of the sun’s rays means that for high latitudes, no part of the daily rotation takes them into shadow.
Regions of Continuous Daylight
Continuous daylight is observed in regions within or very close to the Arctic and Antarctic Circles, approximately 66.5 degrees latitude north and south. As one moves further from these circles towards the poles, the duration of continuous daylight increases. At the Arctic or Antarctic Circle, the sun remains above the horizon for at least 24 hours on the summer solstice.
Moving closer to the poles, the period of perpetual daylight extends significantly. At the North and South Poles, the sun remains continuously visible for approximately six months. This means the sun rises around the spring equinox and does not set until the autumn equinox. Countries with territories experiencing this phenomenon in the Northern Hemisphere include Norway, often called the “Land of the Midnight Sun,” along with Finland, Sweden, Russia, Greenland, Canada (Yukon, Nunavut, Northwest Territories), and the United States (Alaska).
Life in Perpetual Sunlight
Living in environments with continuous daylight presents unique conditions that influence plants, animals, and humans alike. Plants in these regions often exhibit rapid growth during the summer months to maximize the extended light for photosynthesis. They adapt by increasing their photosynthetic rate and adjusting how they use energy, sometimes storing more sugar as starch to prepare for periods of less light.
Animals in these polar regions also show adaptations to the altered light cycles. Many species, particularly mammals, regulate their annual cycles of reproduction, growth, and metabolism based on the duration of daylight. For example, reindeer have evolved eyes that can utilize more UV light, helping them discern plants in the continuous dim light of the polar summer. While some animals, like arctic ground squirrels, maintain their circadian rhythms during summer, others may stop adhering to a strict 24-hour cycle.
Humans living under the midnight sun often experience disruptions to their natural sleep patterns, as the constant light can interfere with the body’s circadian rhythm, which relies on light-dark cues. Many residents use heavy blackout curtains or eye masks to create artificial darkness for sleep. The extended daylight can also influence mood, with increased sunlight exposure linked to higher serotonin levels, though drastic seasonal shifts can pose challenges for mental well-being. Despite these adjustments, communities in these regions often embrace the continuous daylight with increased outdoor activities and unique cultural celebrations, making the most of the extended “day.”