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

Alaska's location relative to the sun is the reason for its seasonal change in daylight.
Alaska receives the most sun when the North Pole is inclined toward the sun.
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  • Originally Written By: R. Kayne
  • Revised By: C. Mitchell
  • Edited By: Sara Z. Potter
  • Last Modified Date: 24 October 2014
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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

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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.

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.

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aplenty
Post 3

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
Post 2

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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