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why does alaska have 30 days of night

All of Alaska does not go dark in winter! But the further north you go, the darker it gets. On the shortest day of the year (December 21, winter solstice), you ll find a range of daylight hours depending on where you are:
Even though residents of Barrow, the northernmost town in Alaska, won t see the sun for 67 days come winter, they enjoy the midnight sun all summer - over 80 days of uninterrupted daylight. Anchorage enjoys a more modest amount of daylight in summer than Barrow - but that s still a good 19 hours between sunrise and sunset on the longest day of the year, Summer Solstice. The Arctic Circle is the boundary of the true midnight sun.

South of this line the sun rises and sets all year round. Likewise, the gain in daylight as you get closer to the equinox (midway between the solstices) increases as you head further north. On Spring Equinox, March 22: Fairbanks, about 7 minutes Anchorage, about 6 minutes Juneau, about 5 minutes In other words, Anchorage experiences the equivalent of a daylight savings time change every two weeks! Any place north of the Arctic circle or south of the Antarctic circle gets at least one day each where the sun does not set and one where it does not rise at all. During the summer these places will experience at least one day where the sun shines even at midnight and in the winter where even at noon the sun will remain beneath the horizon.

The closer to the poles you get the longer the period without sunrise/sunset will be. At the poles itself you are basically at the point where you have half a year of day in the summer and half a year of night in the winter. Even in non Arctic regions you will still feel a bit of it as you can see the days getting longer in the summer and shorter in the winter. The further away you get from the equator the more pronounced the whole days getting longer/shorter will get.

If you go far enough north or south you will reach a point where the longest day / longest night is actually longer than 24 hours. At that point rather than setting the sun will only come close to the horizon but never set entirely or never actually rise entirely. The reason for this has to do with the axial tilt of Earth. The earth axis goes through the poles. If it was perfect perpendicular to the direction in which the sun is, we would always get 12 hours of day and night everywhere. Since the axis is tilted, the parts that are tilted towards the sun get more light and the parts tilted away from it get less (this is how we get summer and winter).

Beyond the polar circles this gets so extreme that at some points even when you are technically on the far side of earth from the sun you still get sunlight. (Or still get no sunlight when you are technically on the day sight in the winter). the whole business with the axial tilt may be hard to grasp but the important bit is that days are longer in the summer. The closer to the poles you get the greater this effect is (longer days in new England than Florida) and if you get close enough to the poles the longest day will be so long that it lasts more than a day.

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