Shortest Day vs. Earliest Night
I am always happy to celebrate the decision of our sun to return to a higher point in our northern sky, a decision it routinely takes about this time of year: 21 December. It seems so delightful that the days seem to start getting longer immediately it makes the decision.
And then, whenever the topic comes up, as it certainly has today, I always make a pest of myself by pointing out my favorite astronomical fact for those of us in the northern hemisphere: although the winter solstice marks the shortest amount of daylight in the year, the earliest sunset of the year actually happened three weeks ago, on 7 December. The last time I mentioned it in this space (in 2006) I didn't have any really good, clear explanation to offer and I don't this time, either. I posted a few links previously — look at them if you feel yourself the intrepid explorer of orbital dynamics — but for now we'll just wave our hands and say it's because of the tilt of the Earth, and the fact that it's roughly spherical (at least, I think this would not happen if the Earth were cylindrical along its axis of rotation).
But anyway, the point I always make is this: by the time we get to the solstice, the sunset is already getting noticeably later and psychologically (to me, at least, since I rarely encounter sunrise) this makes us feel the day is getting longer at a rather brisk pace once the solstice is passed. The reason for that sensation, of course, is that it started three weeks ago. (Have fun verifying this for yourself with the NOAA Sunrise/Sunset calendar.)
For those who key on the sunrise to judge the length of their day–I'm sorry, but the latest sunrise falls on 7 January.
In: All, It's Only Rocket Science, The Art of Conversation
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on Tuesday, 22 December 2009 at 12.07
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Here on the West Coast, a little south of the 49th parallel, our earliest sunset occurs December 10-12. Our sunset today is already four minutes later. Sunrise, of course, is a different matter. It still has one minute to go before it reaches its latest time. The National Research Council of Canada gives our sunrise time as 0805 from December 26 to January 5. I'm presuming that the latest sunrise comes somewhere in the middle of that period (which is also eleven of the Twelve Days of Christmas). By contrast, sunset on January 5 is already 16 minutes later than it was December 11.
The newish moon with, I think, Jupiter in fairly close proximity, was quite lovely in the south-western sky last night.
on Wednesday, 23 December 2009 at 04.00
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Fascinating. I had no idea the earliest sunset occurred so early in December. I was also under the impression days don't start getting longer until we're past the solstice. Live and, thanks to you, learn.
For whatever reason, my wife and I don't start remarking about the days becoming noticeably longer until the second half of February. That might be because we're not so sensitively attuned to these things. But I think it also has to do with the fact that we rarely have clear skies in January and the first half of February. Mostly, they're overcast, at least, and dark, dreary and fog laden at worst. So, comes a day later on in February when the afternoon sky is clear, and it seems all of a sudden that daylight lingers dramatically longer than the last time we can recall that happening.
on Thursday, 24 December 2009 at 06.02
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It appears that earliest sunset/latest sunrise is latitude/longitude dependent.
I recall a political discussion I had with a Canadian high school science teacher. I rattled him a bit with my evisceration of the welfare state etc. so he swerves into a disquisition about the orbital mechanics of earliest sunset/latest sunrise. There is something grand and majestic about celestial mechanics that gets one's mind off of politics.