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As solstice approaches, a look at why Alaska has the most daylight

From Ketchikan to Barrow and everywhere in between, the abundance of daylight in summer affects Alaskans' lives in countless ways -- mostly positive. From construction to recreation to travel, we use the blessing of daylight to conduct activities unfathomable to our Lower 48 counterparts.

Some say it is our reward for a long, dark winter. Perhaps.

Why do we receive so much daylight? The Earth makes a 365-day orbital journey around the sun. While orbiting the sun, we are tilted about 23 degrees from a straight up and down position. The tilt keeps our planet pointed in the same direction all year long as we move around the sun. During the summer months in the northern hemisphere, the Earth faces toward the sun. In the winter, the opposite is true. The day we're most directly pointed toward the sun is the summer solstice, the longest day of the year. Summer solstice is always June 20 or June 21.

How much daylight is there on the summer solstice? That depends on where in Alaska you live. The farther north you go, the longer the day. Just north of Fairbanks, the day is 24 hours long. In Fairbanks, there are nearly 22 hours of daylight, about 19.5 hours in Anchorage and 18.2 hours in Juneau.

Keep in mind that these numbers represent the amount of time the sun is above the horizon. If we include civil twilight, an amount of light that is enough to function without assistance if no clouds are present, the 24-hour line drops to the latitude of Kenai. In Anchorage, all days between June 8 and July 5 have 24 hours of daylight or civil twilight. Fairbanks has more than 70 days with 24 hours of daylight or civil twilight.

What about winter?

But down in Juneau, there are no days with 24-hour daylight/civil twilight.

When I tell people how much daylight there is in an Alaska summer, a common response goes something like this, "Yeah, but you make up for it in the winter."

That's only partially true. If you add up all of the daylight throughout the course of the year, every place in Alaska receives more daylight than every place in the Lower 48.

There are two reasons for this. First, sunrise occurs when the top of the sun's disk rises above the horizon in the morning and sunset similarly occurs when the top of the sun's disk drops below the horizon in the evening.

At high latitudes, the sun traces a more diagonal path so the time it takes for the sun's disk to clear the horizon is longer than more southerly latitudes -- where the movement is more straight up and down.

Second, the Earth moves around the sun more slowly in the summer because the distance between the Earth and the sun is slightly greater. This causes the sun to stay near its highest position in summer for a longer period of time than its corresponding lowest position in winter.

Barrow, for example, has 79 days in summer with no sunset but only 61 days in winter with no sunrise.

219 hours more

Due to the effects listed above, the peak location for the most annual daylight in the northern hemisphere is right at the Arctic Circle; which over the course of a year receives an additional 219 hours of daylight compared to the equator.

It gets even better, though. If we include civil twilight, the coastal plain north of the Brooks Range is the big winner. That area gets 828 hours more annual light hours (daylight plus twilight) than the equator. Again, this is a function of the diagonal track of the sun and the slower orbital movement in the summer.

Finally, the slower orbital movement means that the northern hemisphere receives slightly more light than the southern hemisphere at all latitudes. Therefore, not only does northern Alaska beat the Lower 48 for light, it also beats anywhere in the southern hemisphere.

So the next time someone complains about Alaska's dark winter, be sure to tell them that we are not only the biggest, but we are also the brightest.

Brian Brettschneider is an Anchorage-based environmental planner and climatologist who writes an Alaska weather blog on Facebook.

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