Friday 17 April 2015
defining twilight
One of the things that surprised me most when I moved to Fairbanks two Decembers ago was how it was never really bright out. It always looked like sunrise, or sunset, but never quite day. The sun is only up for a short period of time, and it arcs around the sky without ever climbing very high.The saving grace is that its actually light for quite a while before the sun comes up and after it sets. There are words for that! I just learned them last week, and pass them along now as terms to define what anyone whos lived here has known all along.
Civil twilight, from heavens-above.com, is "The time after sunset and before sunrise when the Sun is below the horizon but not more than 6° below it. . . [T]he sky is still quite bright and only the very brightest stars and satellites can be seen."
Nautical twilight is when the sun is between 6 and 12 degrees below the horizon. The brighter stars used for navigation have come out, but the horizon and general shapes of things can still be seen.
Another thing about sunlight. With such a big spread between summer daylight hours and winter, the rate of change is quick. Were losing about 7 minutes a day now, or close to an hour a week.
In news, the LA Times had a story on dealing with erosion in Kivalina. And Gore got to talk with Bush . . .
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