Alaska is known for its vast wilderness and extreme light cycles. Many are curious about the extent of darkness in this northern region, especially during winter. Alaska’s light conditions are more nuanced than perpetual night, encompassing varying degrees of dimness and short daylight periods depending on location.
The Astronomical Reasons for Alaska’s Light Cycles
Alaska’s unique light patterns stem from astronomical principles. Earth’s axis is tilted 23.5 degrees relative to its orbit around the Sun. As Earth revolves, this tilt causes different parts of the planet to receive varying amounts of direct sunlight. During the Northern Hemisphere’s winter, the Arctic region, including much of Alaska, angles away from the Sun.
This orientation keeps the Sun below the horizon for extended periods in northern latitudes, resulting in shorter days and prolonged darkness. The closer a location is to the North Pole, the more pronounced this effect. This alignment is responsible for polar night in the most northern areas.
Understanding Different Levels of Darkness
When discussing darkness in Alaska, it is important to distinguish between levels of ambient light. True darkness, where no direct sunlight is visible, is distinct from twilight. Twilight occurs when the Sun is below the horizon but its light still illuminates the atmosphere.
Civil twilight is the brightest phase, with the Sun 0 to 6 degrees below the horizon. During this time, there is enough natural light for outdoor activities without artificial illumination. Nautical twilight follows, with the Sun 6 to 12 degrees below the horizon; artificial light is often needed, though the horizon may still be discernible. Astronomical twilight is the darkest phase, defined by the Sun being 12 to 18 degrees below the horizon, after which the sky is considered fully dark for astronomical observations.
How Much Darkness Each Region Experiences
The amount of darkness in Alaska varies significantly by latitude. Utqiagvik, the northernmost city in the United States, experiences the most extreme conditions. Located above the Arctic Circle, Utqiagvik undergoes polar night, where the Sun remains below the horizon for about 64 to 67 days, typically from mid-November to late January. Even during polar night, Utqiagvik is not in absolute pitch blackness; it still experiences several hours of civil twilight each day, offering a dim glow similar to dawn or dusk.
Further south, Anchorage, the state’s largest city, has approximately 5.5 hours of daylight around the winter solstice. Fairbanks, located in the Interior of Alaska, experiences even shorter days, with only about 3 hours and 40 minutes of daylight during the winter solstice. Juneau, situated in the panhandle, has relatively more daylight than its northern counterparts, with about 6 to 6.5 hours of daylight on the winter solstice. These variations highlight how latitude directly influences the duration of light and darkness across the state.
The Peak of Winter Darkness
The most intense period of darkness in Alaska centers around the winter solstice, which occurs annually on or around December 21. For regions above the Arctic Circle, like Utqiagvik, this period represents the heart of the polar night, where the Sun does not rise above the horizon at all. While not completely dark, the light available is limited to the various twilight phases, especially civil twilight, which provides a brief, muted illumination.
As the solstice passes, the duration of daylight gradually begins to increase, though the change is very slow initially. In places like Fairbanks, where the Sun barely arcs above the horizon during the solstice, the short daylight hours mark the deepest part of winter’s darkness. This gradual return of light signals the slow transition towards longer days.