Why Does Alaska Have Really Long Days during Some Times of the Year and Really Short Days during Other Times?

R. Kayne
R. Kayne
The Earth spins on a fixed axis, but the inclination means that there are times when Alaska gets much more exposure to the sun and other times when it receives much less.
The Earth spins on a fixed axis, but the inclination means that there are times when Alaska gets much more exposure to the sun and other times when it receives much less.

Alaska typically has really long days during some times of the year and really short days during others as a result of its location in the far north, near the North Pole. This puts it very near the earth’s northernmost axis, which brings it closer to the sun when the earth tilts one way, but much farther from it when it tilts the other way. Alaskan summer days tend to be very long as a result, and in some regions the sun never sets; in the winter, though, it may never rise, or come up for only a few hours at a time. Most of the regions on the opposite side of the earth, down at the South Pole, experience very similar seasonal shifts on an inverse schedule. When Alaska is having long summer days, Antarctica and the islands surrounding it typically experience the darkness of winter, and vice versa.

Visualizing the Axis

Alaska receives the most sun when the North Pole is inclined toward the sun.
Alaska receives the most sun when the North Pole is inclined toward the sun.

The axis or tilt of the earth is what primarily accounts for the extraordinary periods of daylight and darkness at the poles because it is during these times that the land in the northern part of Alaska is tilted either directly into or far away from the sun. People often find it easiest to understand this by making or imagining a model. In the center is a sphere, like a tennis ball, with a long needle passing through its center from top to bottom. The needle extends out both “poles” creating an axis. A black line should run the circumference of the ball to indicate its “equator.” If that ball is placed on a roughly circular track and the axis is inclined 23.5 degrees towards the track, it will mimic the earth to a pretty close degree. A light source in the center will represent the sun.

Alaska's location relative to the sun is the reason for its seasonal change in daylight.
Alaska's location relative to the sun is the reason for its seasonal change in daylight.

As the ball moves around the track, its axis remains fixed, though by virtue of it moving around the track its inclination, relative to the center light, changes. At one point the northern pole gets greater exposure to the light. At the opposite end, though, the same northern region is pointed away from the light source with the southern pole exposed inward.

Understanding Seasonal Shifts

Some people mistakenly attribute seasons to the slightly elliptical orbit of the earth, believing that the closer the earth is to the sun, the warmer the days will be. In reality, earth’s orbit is nearly circular, and the small deviation in distance is not enough to cause seasonal change. The length of a day at any time of year is predominantly a factor of how close a certain location is to either of the earth’s two axes. The equator, where the seasons don’t really change and things tend to stay pretty warm, is usually the farthest point from either pole. As a result, inclination and tilt don’t make much of an impact here. Things tend to get more extreme the further north or south one goes.

Inclination During the Summer and Winter

This inclination of the earth is what creates the seasons, and is also responsible for Alaska's long summer days. When the North Pole is inclined inward towards the sun, the region receives extended exposure. From the viewpoint of someone standing at true north on the summer solstice, the sun raises high into the sky, and then circles the horizon without ever setting. Elongated exposure to sunlight during the summer allows the region to retain more heat. Shadows are shorter because the sun is higher overhead.

At the South Pole in Antarctica, the opposite is occurring. Here, the region is inclined away from the sun, so that on the winter solstice the sun skirts the horizons but never quite rises. In outlying regions further from “true south” where the sun does raise low in the sky for short periods of time, the sun’s angle is very oblique. This creates longer shadows, additional atmospheric filtering, and weaker radiation or warmth. Thus, when Alaska is experiencing endless summer days filled with direct light, heat and warmth, desolate Antarctica is steeped in days of near total darkness and weak sunlight. Conversely, when Antarctica sees summer, Alaska is having winter.

Differences for Spring and Autumn

In spring and autumn the earth’s axis is aligned along its orbital path rather than towards or away from the sun. Hence, the sun shines most directly on the equatorial regions, or center of the earth. On the solstices that mark these seasons — March 21st and September 21st, respectively — most regions have 12-hour days and 12-hour nights. For each day that passes after a spring or fall equinox, the days begin lengthening in one hemisphere and shortening in the other.

Considerations Regarding Location

It’s important to note that the state of Alaska is very large and covers a great deal of land. While some of the northernmost parts are within the Arctic Circle and sit very near the North Pole, there are many other parts of the state that sit much further south. As a result, seasonal generalizations can’t really be made for the state as a whole. Many Alaskans in the southernmost regions never see sunlight that lasts all night or winter days of total darkness.

How Long Does it Stay Dark in Alaska?

Alaska is the largest state in the United States, measuring 663,300 square miles. For comparison, that is more area than the next two largest states, California and Texas, combined. The region is so extensive that it makes up multiple different climate zones ranging from maritime to continental to arctic. Due to its size, the number of hours of darkness in Alaska varies widely depending on location. Only the northernmost area of the state undergoes the extremes of daylight and dark that many mistakenly associate with the state as a whole.

What Are Alaska Winter Daylight Hours?

The longest period of darkness in the state occurs during the winter solstice which falls near December 21 each year. The most southern areas of the state never experience the total darkness that Alaska is known for. Conversely, towns in the far north of the state experience long periods of complete darkness. Here is a sampling of the wide variety of daylight hours in Alaska during winter solstice:

  • The city of Juneau, located in Alaska's southern panhandle, has around six hours of daylight even at the height of winter, with sunrise occurring at 8:45 a.m. and sunset following at 3:07 p.m.
  • Centrally located cities such as Fairbanks see the sun rise at 10:42 a.m. and set at 2:41 p.m. giving them less than four hours of daylight.
  • Utqiaġvik, Alaska's northernmost town, watches the sunset around November 18 and does not see a sunrise again until late January; a total of 67 consecutive days of darkness.

The Effect of Long Term Darkness

Statistically, Alaskans experience less major depression than the residents of many other states. However, about 10 percent of Alaskans are impacted by seasonal affective disorder, a type of depression linked directly to insufficient exposure to sunlight. That is double the average percentage of residents experiencing SAD in other states.

Seasonal affective disorder may also be a contributing factor to the rampant levels of alcohol and drug abuse in the state. Studies estimate that an astounding 50% of Alaska residents engage in some level of binge drinking and the state ranks among the top 10 states for severe drug use. In the under-served and isolated Native populations, these statistics are even starker.

During the winter months, many Alaska residents use bright light therapy to combat the persistent darkness. They may also increase supplementation of vitamin D as well as the use of prescription anti-depressants.

What Are Alaska Summer Daylight Hours?

Just as the amount of darkness in winter varies, so do the hours of daylight in the summer. The north gets the most extreme daylight exposure while the south experiences some hours of twilight-like darkness. Using the same sampling of locations, this is a snapshot of the state on the June 21 summer solstice:

  • In the southern city of Juneau, the sun will rise at 3:51 a.m. and remain in the sky until 10:07 p.m., 18 hours later.
  • Centrally located Fairbanks will get over 20 hours of daylight, with sunrise occurring at 2:59 a.m. and sunset at 12:57 a.m.
  • The far northern town of Utqiaġvik begins its 80 day stretch of round-the-clock sunlight on May 10. It won't see a sunset until early August.

The Effect of Long Term Daylight

Overwhelmingly, Alaskans love the state's long days during the summer months. Many residents embrace the ability to engage in activities whenever their schedule allows and engage in outdoor activities at all hours.

The biggest issue with the constant daylight is making the adjustment to sleeping when it isn't dark. The prolonged daylight hours can throw off the body's circadian rhythms making sleep difficult to attain. Some residents make use of blackout curtains, others may utilize sleep masks to trick the body into thinking it is dark. The majority of locals and visitors report adjusting to the long days quickly and easily.

Does Alaska Have All Four Seasons?

Although locals often joke about Alaska only having two seasons, the state does have both spring and autumn. Both seasons tend to be very brief, sometimes lasting only a couple of weeks. Additionally, the rapidly changing daylight hours can make these seasons challenging to navigate.

On the spring and fall equinox, Alaska comes closest to the average day length of other states with the day split evenly between daylight and dark. Leading into both seasons, however, the daylight hours change drastically on a daily basis. The changes are so rapid that the hours of sunrise and sunset can be a full hour earlier or later each successive week.

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Discussion Comments

aplenty

I think you are talking about the Milankovitch cycles. The Milankovitch cycles, Albedo, and the greenhouse gas effect are what regulate natural climate change. The Milankovitch cycles are the natural cycles in the earth's rotation where it moves from an almost circular orbit to a more elliptical orbit around the sun. The earth changes its orbit, its vertical axis, and its tilt in normal cycles over periods of hundreds of thousands of years. I hope this helps point you in the right direction.

FrameMaker

I understand how the change in the length of day’s work between seasons. What I do not understand is how natural cycles of solar radiation work. I hear talk about this all the time in regards to climate change, and I want to know how this works. What long-term cycles create the longer and shorter days at the poles, which in turn influences the amount of polar ice and overall climate?

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    • The Earth spins on a fixed axis, but the inclination means that there are times when Alaska gets much more exposure to the sun and other times when it receives much less.
      By: aopsan
      The Earth spins on a fixed axis, but the inclination means that there are times when Alaska gets much more exposure to the sun and other times when it receives much less.
    • Alaska receives the most sun when the North Pole is inclined toward the sun.
      By: miiko
      Alaska receives the most sun when the North Pole is inclined toward the sun.
    • Alaska's location relative to the sun is the reason for its seasonal change in daylight.
      By: juan35mm
      Alaska's location relative to the sun is the reason for its seasonal change in daylight.