The Midnight Sun, or Polar Day, is a natural phenomenon where the sun remains visible for a full 24-hour period. This seasonal occurrence is limited to the planet’s highest-latitude regions. Continuous illumination is experienced during summer months in areas north of the Arctic Circle and south of the Antarctic Circle. Since this geographical boundary crosses multiple nations, several countries experience this unique event.
The Astronomical Reason for Perpetual Daylight
The Midnight Sun is caused by Earth’s orbital path combined with the 23.5-degree tilt of its rotational axis, which is responsible for the changing seasons.
During the Northern Hemisphere’s summer, the North Pole is angled toward the sun, causing the Arctic Circle region to be continuously bathed in sunlight. As the Earth spins, the sun never dips below the horizon for observers in these far northern locations.
The Arctic Circle, located at 66.5 degrees North latitude, marks the boundary where the Midnight Sun is visible for at least one day during the summer solstice. The period of continuous daylight increases closer to the North Pole. At the pole itself, the sun remains above the horizon for approximately six months.
The phenomenon peaks around the summer solstice, typically June 21st. Afterward, the duration of daylight gradually decreases until the sun sets again. The sun traces a low, circular path across the sky without disappearing below the horizon line.
Countries Experiencing the Midnight Sun
Many nations and territories have land extending into the Arctic Circle and experience the seasonal Midnight Sun. Norway is a prominent example, with a large section of its territory in the Arctic region. In the Norwegian archipelago of Svalbard, the sun does not set from late April until late August.
Neighboring Nordic countries also experience continuous daylight. Sweden’s northern Lapland region, including towns like Kiruna, has periods of no night during the summer. Finland sees the sun remain above the horizon for over 70 days in its northernmost areas.
Greenland, an autonomous territory of Denmark, is almost entirely within the Arctic Circle. While most of Iceland lies just south of the Arctic Circle, the northern island of Grímsey is crossed by the line, resulting in long twilight hours where the sun barely dips below the horizon in late June.
The phenomenon is also seen in North America and Russia. The United States experiences it in Alaska, particularly in northern cities like Utqiagvik. Canada’s northern territories, including Yukon, Nunavut, and the Northwest Territories, also lie within the Arctic Circle. Russia’s expansive northern territory, including the city of Murmansk, sees the sun stay up for weeks at a time.
The duration of the Midnight Sun varies greatly across these countries, ranging from a single day near the Arctic Circle to multiple months in the most polar regions.
The Impact of Constant Light on Human Health
Continuous exposure to daylight presents a challenge to the human body’s internal timekeeping system. The 24-hour cycle, known as the circadian rhythm, is regulated by light and darkness cues. Constant light disrupts the natural synchronization of this biological clock.
This disruption primarily suppresses melatonin, a hormone that signals the body to sleep and promotes drowsiness. Since light inhibits melatonin production, the brain does not receive the necessary chemical signal to initiate and maintain sleep. This often leads to fragmented sleep, reduced restorative deep sleep, and chronic insomnia among residents and visitors.
To cope with the unending daylight, people rely on behavioral adjustments to create an artificial night. This includes using heavy blackout curtains or specialized eye masks to block external light during sleeping hours. Exposure to even moderate light levels during traditional nighttime can negatively affect cardiometabolic function and increase heart rate.
Chronic misalignment of the circadian rhythm due to the Polar Day-Night cycle has been linked to mood alterations and cognitive deficits. While bright summer light can boost mood in some individuals, the lack of a proper dark phase places a strain on the body’s metabolic and neurological systems. Dark conditions are necessary for biological rest and repair.