Daylight Hours at 61 Degrees Latitude: The Half-Assed Astronomy Lesson Nobody Was Asking For

A common question asked to us by people who have not yet visited Alaska (or those who have but somehow timed their visit to roughly coincide with an equinox) is some version of the one about how long the days are at different times of the year. One way to answer this - favored by some of the particularly engineery engineers that I used to work with - is to say, "Every day everywhere is 24 hours - that's how long it takes for Earth to complete one full rotation about its axis." This is met with the superlative kind of eye-roll typically reserved for reaction to a sixth-grader carrying around a book of language trivia and testing out newly-learned smart-ass grammar gotchas like how he can put his plate in the dishwasher but you never asked if he would. The question is of course not intended to be about the length of the midnight-to-midnight stretch (which has a fun technical name that I totally would have Balderdashed to instead be some sort of dragon) but rather how much of that period is comprised of daylight, the variance in which is admittedly kind of interesting and different from the Lower 48 but not as different as people might think.

Executive Summary

The shortest day of the year is December 21 (everywhere in the Northern Hemisphere). On that day in Anchorage, the sun rises at 10:14 AM and sets at 3:42 PM; dawn to dusk is more like 9:30 to 4:15. The sun arcs shallowly across the south horizon and spends a good part of the morning hidden behind the mountains, making the days feel even shorter; in late December, we can't see the sun at our house until almost noon.

The longest day of the year is June 21 (also everywhere in the Northern Hemisphere).  On that day in Anchorage, the sun rises at 4:21 AM and sets at 11:42 PM, but even at 2:00 AM the sky is not anything that I would call "dark". The sun rises in the northeast, traveling elliptically around the south sky and eventually down to the northwest before ducking behind the north horizon for a few hours.

Every day in between is something in between.

Thanks for reading! Here is a link to Google for continued internet browsing.

Totally Unnecessary Exposition (Optional Reading)

Why does the length of daylight vary throughout the year? If you're like me, you probably learned this sometime in middle school but then sort of forgot about it when you didn't have a reason to think about it every day, until you found out you had to move to Alaska and started vaguely recalling it while frantically researching whether you would ever again see the sun in January, and after about a year-and a-half of getting asked about it a lot you also (separately) just happened to have recently started writing this themeless blog with no self-imposed restrictions on subject matter, which seemed like a great place to write an indefensibly long post about it that probably could have just been two sentences with one picture and maybe a link to Wikipedia.

In simple terms - I do not mean this in a patronizing, "let me see if I can dumb this down" way, but more of a "I am almost certainly about to omit some critical nuance that I am not aware of or do not understand" way - two primary things affect the amount of sun exposure a given place on Earth sees on a given day: the latitude of the place and the tilt of Earth's axis.

If the axis of rotation were not tilted (it is - PAY ATTENTION - but if), things would be simple. Every place on the planet would have 12 hours of daylight and 12 hours of night every day of the year because every place would spend half of each day on the light side of the globe and half on the dark side. Also, the apparent arc of the sun in a given place would be exactly the same every day of the year: at the equator, the sun would appear to arc directly overhead every day; in Alaska, it would follow a consistent year-round arc closer to the South horizon. This result of consistent daylight hours + consistent sun angles would be no seasons - for any given place, weather would be effectively the same in June as it is December.

But the axis is tilted relative to the plane of Earth's orbit around the sun, so everything changes slightly throughout the year. This is explained well enough here (Go Wolfpack!), including several useful pictures that are remarkably similar to the ones I was originally intending to produce myself until it became apparent that doing so would be quite redundant if considering the entirety of the Internet, never mind my eventual realization that this is not a textbook or PowerPoint presentation and that my time might be better spent on, like, laundry.

The takeaway is that the Northern hemisphere is pointed more directly towards the sun during a certain part of the year. We call this "summer". This change in astronomical perspective affects both the apparent angle of the sun relative to the horizon (when a spot is pointed more directly at the sun, the sun appears to travel more directly overhead of that spot) and the amount of time the sun is visible in the sky (a larger portion of the spot's path around the globe - i.e. that spot's day - is illuminated). This effect is magnified as you move further from the equator such that things get wacky at the poles: in the region from the North Pole to 66.5622° degrees latitude - the technical definition of The Arctic - there is a stretch of the summer during which the entire path around the globe is lit by the sun, meaning that the sun never sets. The opposite is true in winter, when the Arctic is entirely on the dark side of the globe and the sun never rises.

Anchorage's latitude (~61.2 degrees N) puts it just below this area, such that constant daylight or darkness never quite happens, although it comes close. The longest summer day sees only about 4 1/2 hours of "darkness", during which the twilight lingers and it is still light enough outside to read a newspaper but perhaps not to track down a fly ball. This is interesting and fun in ways that I have anecdotally described elsewhere, but it is also a little disconcerting being outside after dinner and a few drinks (or worse, leaving a dark bar) and feeling so tired in broad daylight. It is reminiscent of taking a flight from the East Coast to Las Vegas and going straight to a 10:00 PM dinner reservation at a restaurant in one of those indoor promenades made to look like it's outside, with all of your environmental clues suggesting it is early in the evening until you realize it's effectively 1:15 AM and you have been drinking for several hours and no wonder you are falling asleep on your appetizer.

In the winter, the shortest day gets just over 5 1/2 hours of official and legitimate daylight, and although dawn and dusk do bleed a bit into the hours prior to official sunrise and after official sunset, this is not fun. The most unexpected (to me) annoyance of this time of year is the low sun angle: driving south during the daylight hours of winter involves staring directly into a low but surprisingly intense glare:

Southbound driving on clear winter days. This was taken at 1:08 on 12/21/12 - exactly ten minutes after "solar noon" (when the sun reaches its high point over the horizon) on the shortest day of the year.

Strangely, real estate listings here highlight south-facing windows as a huge amenity. We do not have any, but I am not so sure that I would want them. Although I suppose that is what the blinds are for (blocking the natural light you paid extra for).