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Dec. 21 is the darkest day of the year, right? Not so fast
It might surprise you to learn the earliest sunset of the year is not on the winter solstice, also known as the “shortest” day of the year for its measly pittance of daylight.
Winter is still technically still around the corner, despite what the snowy weather and omnipresent holiday jingles would have you think.
That’s because winter’s astronomical start in the Northern Hemisphere isn’t until Dec. 21 — the winter solstice, also known as the “shortest” or darkest day of the year for its measly pittance of daylight hours. As The Old Farmer’s Almanac explains, each season has two start dates: the astronomical start, based on the sun’s position relative to the Earth, and the meteorological start, based on our 12-month calendar and annual temperature cycle. (So yes, by some definitions, winter started last Sunday.)
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But it might surprise you to learn the earliest sunset of the year is not on the winter solstice, despite its dark and gloomy reputation.
The honor of the earliest sunset actually goes to Saturday, Dec. 7, when the sun will set at 4:11 p.m. and 37 seconds, per meteorologist and Boston Globe correspondent Dave Epstein. (According to Epstein, the sun will set a whole one second later on Sunday.)
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“Our sunrises will continue to get later and thus the gap between sunrise and sunset continues to shrink until after the winter solstice in a couple of weeks,” Epstein explained in a Globe forecast earlier this week.
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But in terms of what most people actually experience with daylight, early December is the darkest time of the year, Bob Berman, astronomer editor for The Old Farmer’s Almanac, explained in an article last month.
“Since far more people are awake and aware of things at 4:30 PM than they are at 6 in the morning, in a very real sense, you can forget about the solstice and the official ‘shortest day of the year’ in terms of daylight,” Berman wrote.
The latest sunrise comes in early January, about two weeks after the solstice, Berman noted. Epstein offered an explanation for this phenomenon in a 2020 Globe article: “Sunrise and sunset are asynchronous over the course of the year and don’t change equally. This means although the shortest amount of overall daylight is Dec. 21, that day is neither the latest sunrise nor the earliest sunset.”
As for the science behind this, the U.S. Naval Observatory’s Astronomical Applications Department offers a deep dive into the difference between sun time and clock time. A more concise answer from the National Weather Service offers another explanation for why the earliest sunset doesn’t line up with the winter solstice: “While the length of a day is defined as 24 hours long, in reality, it varies slightly due to the spin of the Earth. The actual length is defined as a ‘solar day,’ and its length can vary from a few seconds to 30 seconds longer than 24 hours.”
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And if those earlier sunsets are bringing on a bad case of the winter blues, there’s always Sen. Ed Markey’s push for year-round daylight saving time (i.e. the later sunsets we’re accustomed to in the summer).
“More sun means more fun,” Markey declared earlier this fall.
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