First, some definitions: Civil Twilight is the time before sunrise or after sunset, when there's still enough natural light to perform normal outdoor tasks. Then sun is between 0-6 degrees below the horizon. There are two other kinds of twilight (nautical and astronomical), but I'll just call the civil one "twilight." Beyond that, I'll just point out that we have some pretty high mountains to our east, so we may not see the sun when I claim the sun "rises," but it's still pretty bright out.
Today, we have 7 hours of daylight (9:16am-4:13pm), but about 8.5 hours including twilight (8:23am-5:06pm). This means I'm walking to and from the bus in darkness, but civil dawn/dusk happens during my commute. For comparison, St Louis today had 10 hours of daylight, or about 11 hours including twilight (6:18am-5:13pm).
We won't be in Alaska for the shortest day of the year (Dec 22, Winter Solstice), but if we were we'd only have about 5.5 hours of daylight (10:14am-3:41pm), or 7.5 hours including twilight (9:11am-4:43pm). Actually, I'm nitpicking here... our shortest day in Alaska this year will only be 5 minutes longer than that! The solstice is the day the sun appears to "stand still" on the horizon, so things don't change very much in the week or two before and after.
For those of you planning to come to visit next year, you probably won't come before the Spring Equinox (Mar 21), when day and night are roughly equal. It's interesting that on that day, although Anchorage and St Louis both have about 12 hours 10 minutes of daylight, Anchorage has about 40 more minutes of twilight.
Finally, if you wait until the Summer Solstice (June 21), you'll get about 19.5 hours of daylight, or round-the-clock including twilight. In fact, the always-at-least-twilight situation lasts from June 8 - July 4. (What, no fireworks?) It actually looks like we'll be back in the "Lower 48" for some of that time, too, although we won't miss it entirely. This is one of the astronomical novelties that made me think about visiting Alaska someday, even before I got the job offer to come up here. (Why does it happen? The Earth is round and has a decent axial tilt. That's it, in a nutshell.)
If you want to explore this more for yourself, go to this site to generate your own sunrise/sunset/twilight calendars for anywhere in the world. But be sure to turn off the extra twilights and other stuff you don't want, lest it get too cluttered.
And in other astronomy news, rock guitarist Brian May of Queen has been named chancellor of Liverpool John Moores University. For those who missed it, he recently completed his PhD on "Radial Velocities in the Zodiacal Dust Cloud," 36 years after beginning the research.
3 comments:
Here's another question...will you be able to see the northern lights from Anchorage?
One of the times that John's boat, (either the John Adams or the Skipjack) was in the artic circle, the crew was given the opportunity to see the lights, but before John got a chance to, a russian sub was detected in the area and they had to submerge.
That stinks!
We should be able to see the Northern Lights when they are very active. Fairbanks, which is about 300 miles North, is a prime site for viewing. The Alaskan Railroad has a "Northen Lights" package, where you take a scenic train up to Fairbanks, stay a couple of nights to view, then fly back. I would like to do that before we leave!
Happy Thanksgiving!
This is the site I look to for my aurora-predictions:
http://www.gedds.alaska.edu/AuroraForecast/
As I write this, it says the aurora-score is 3 (Moderate), meaning that Anchorage and most of southern Alaska should be able to see the northern lights on the horizon. Of course... (sticks head outside)... it's cloudy here tonight.
As the score goes up, the polar donut of aurora visibility gets wider, and places further and further south get to see them overhead. I think Anchorage starts to see them overhead when it gets to 4 or higher. Not that we've seen any yet...
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