Today, as you probably didn’t know, will the earliest sunset of winter. Tomorrow’s sunset will be a teeny bit later than today’s, which is weird, because winter solstice, the shortest day of the year, doesn’t arrive for two weeks. So what gives?
Our clocks, that’s what.
The Earth doesn’t travel around the sun in a perfect circle, as you may recall from high school physics. (“Kepler’s Three Laws of Planetary Motion” – ring a bell?) As a result, the planet speeds up and slows down slightly over the course of its annual trip. This means that the actual amount of time between one high noon to the next high noon changes slightly during the year; most of the time it isn’t exactly 24 hours most of the time.
It would be a real pain to adjust our clocks slightly every day to factor in this change, so we average it out. This produces a slight discrepancy between noon on our clocks and actual noon when the sun is highest in the sky, as well as between our clocks and other solar moments.
The discrepancy becomes obvious at times like the solstice, when we make careful comparisons between solar events and the hands on our clock. Even then, it’s just an anomaly produced by choices about measurement, not anything to worry about.
The total amount of daylight on the Dec. 21 winter solstice is about nine hours in Concord, a figure that fluctuates slightly from year to year. (This year, it’s officially 8 hours, 58 minutes and 49 seconds from sunrise (7:15 a.m.) to sunset (4:14 p.m.).)
The latest sunrise of winter actually happens until two weeks after the solstice: 7:14 a.m. on Jan. 5, 2016.
And the earliest sunset of winter happened two weeks earlier: 4:11 p.m. today. I hope you celebrated!
Return to the Concord Monitor
I’ve “celebrated” this milestone for years now. Confounding my friends with the (admittedly tongue-in-cheek) claim that after this, the days start getting longer.
Without ever having done any of the math or geometry, I’ve always thought this was the result of the fact that sunset and sunrise are measured not according the *center* of the sun’s disk, but from the *top edge*. Thus making the day/night durations not symmetrical.
Whatever the cause, this date is a comfort to me in coping with these dark days of fall/winter.