Because of the tilt of the earth, northern latitudes experience greater extremes of daylight throughout the seasons — longer days in the summer, shorter days in the winter. So, for me, one of the biggest shocks of my move from the D.C. area to northern Minnesota turned out not to be cultural, but celestial.

In June, the sun doesn't set in Red Lake Falls until close to 9:30 p.m. Add in twilight, and the skies here stay light until well after 10 p.m. during the summer months — a full hour later than what I was used to in the D.C. area.

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Now, of course, we're experiencing the opposite. The sun sets at 4:30, and doesn't rise again until after 8 a.m. On the year's shortest day we'll get about 8 hours 23 minutes of daylight here, about an hour less than D.C. can expect.

This summer, Alaska-based climatologist Brian Brettschneider created a series of fantastic maps illustrating how daylight hours change with latitude. The one most pertinent to today's predicament is below: the number of daylight hours during the winter solstice, the shortest day and longest night of the year.

In the continental U.S. alone, there's more than a two-hour difference in daylight length between the southernmost places (for example, Key West, Fla.: 10 hours 36 minutes) and the northernmost ones (such as Warroad, Minn.: 8 hours 14 minutes).

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Another fun exercise for today is to look at the difference in daylight hours between the summer and winter solstices.

Here in northern Minnesota the summer solstice sun is up for about eight hours longer than the winter solstice sun. In D.C., there's a difference of about 5½ hours between the two. In places like Honolulu there's not much of a difference at all.

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All of this is fun to explore and think about as kind of a climatological curiosity. But these changes in daylight hours do have real, concrete effects on how we live our lives.

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For instance, there's a distinct south-to-north gradient in Google searches for “seasonal affective disorder” which you can see in the map below.

Generally speaking, more exposure to sunlight makes us happier. Those Google results suggest that folks living at higher latitudes may be at higher risk for seasonal depression.