Welcome the Sun!
This is the day of the year, 7 December, when I celebrate my own festival of light to welcome the return of the sun.
No, it is not the shortest day of the year, the day with the least amount of sunlight where I am (about 39 degrees north, 76 degrees, 46 minutes west — but the effect only depends on latitude), because it is not the Winter Solstice, which occurs about 21 December.
It is, however, the earliest sunset of the year, a more interesting inflection point. Since I rarely experience sunrise, at least by choice, this is psychologically much more important. Beyond today, the day will appear to me ever so slowly to be getting longer again because after today the sun will start going down later in the evening.
The effect is hardly noticeable at first,* but by the time we get to the Solstice the day-to-day change in sun-setting time will be noticeably larger. I was happy when I learned about this, the pre-Solstice early-sun-setting day, because it explained for me the feeling I'd always had that once we got past the Solstice it seemed as though the days started getting longer very quickly.#
The reason for the phenomenon is tougher to explain than to comprehend; I looked at three different versions (one, two, and three), none of which struck me as entirely satisfactory, but feel free to have a go. To make a long story short, I can point out that if the earth weren't tilted then this curious misalignment of times wouldn't happen. But then, neither would the seasons, and neither would the apparent position of the sun's zenith in the sky** change from day to day.##
Regardless of all that, I'm always happy to see the sun starting to linger longer at the end of each day.
———-
*For those with a calculus vocabulary, the curve of earliest sunset times as a function of date has just passed an extremum and the derivative is still very near zero.
#Finally, this gives you something to do with those previously useless reports in the newspaper or in the nightly weather forecast that give you sunset and sunrise time: plot the curves for yourself and see when the minima and maxima in sunset and sunrise occur at your latitude.
**Known as the "analemma", the figure-8 shape found on precision sun-dials and on globes of the Earth.
##How much it changes day-to-day depends on one's latitude and is described by the grandly named "Equation of Time".
In: All, It's Only Rocket Science, The Art of Conversation
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on Friday, 8 December 2006 at 00.58
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Hi Jeff. I too have noted that the earliest sunset occurs before the solstice. Here in Victoria the earliest sunset is 1618 on the 11th of December (with '1618' given in the charts as sunset time for both the 10th and 12th as well). The good news is that the evenings start getting longer, and by Christmas day the sun is setting five minutes later, at 1623.
The bad news is that the sunrise keeps getting later until December 27, and then holds at that latest minute (0805 here) until January 5. To me it seems to take forever for the mornings to start advancing.
Not sure what you have available for the USA, but in Canada we have this very handy reference: http://www.hia-iha.nrc-cnrc.gc.ca/sunrise_e.html.
If you want to have some fun with changes in sunrise/sunset times, go to the the "sunrise/sunset for a full year' on the advanced options page, and type in Alert NU.
on Friday, 8 December 2006 at 01.40
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Thanks for the information, Bill. Indeed, although I was going to mention it, I completely forgot to say that the latest sunrise comes about 2 weeks after the Solstice, depending on latitude. No doubt it slipped my mind since I so rarely see the sunrise with any conscious awareness.