Today’s question is….when is the earliest sunset of the year?
Well…most people think it’s on the winter solstice.
And that’s true, in term of popular belief, even if, actually, the darkest days are actually right now, in early December!
Winter solstice is the shortest day of the year in terms of daylight, but it does not have the latest sunrise nor the earliest sunset of the year.
Yes, it offers the shortest period of daylight.
But, unless you live close to the Arctic Circle or Antarctic Circle, your earliest sunsets aren’t on or even near the solstice itself.
Instead, your earliest sunsets will come before the winter solstice.
For many folks in North America as well as in Europe, this is a dark time of year and the sunsets come exceedingly early.
Probably It might surprise you to know that the earliest sunsets come several weeks before the winter solstice, and not on the solstice itself, as many would guess.
This puzzles people, but it’s actually a really reliable yearly sequence.
To understand it, try thinking about it in terms of solar noon or midday, the time midway between sunrise and sunset, when the sun reaches its highest point for the day.
A clock ticks off exactly 24 hours from one noon to the next. But the actual days – as measured by the spin of the Earth – are rarely exactly 24 hours long.
So the exact time of solar noon, as measured by Earth’s spin, shifts in a seasonal way. If you measured Earth’s spin from one solar noon to the next, you’d find that – around the time of the December solstice – the time period between consecutive solar noons is actually half a minute longer than 24 hours.
So, two weeks before the solstice, for example – the sun reaches its noontime position at 11:52 a.m. local standard time, or the time on your clock wherever you are around the globe. Two weeks later, on the winter solstice, the sun reaches its noontime position at 11:59 a.m. That’s 7 minutes later.
In short, first comes the earliest sunset, in early December.
Then there’s the winter solstice half a month later, on December 21 in the Northern Hemisphere, basically the day with the fewest minutes of daylight.
Finally, another two weeks later, in early January, we have our murkiest morning, the latest sunrise.
At this point we’re right now at the low point of afternoon sunshine and, since far more people are awake and aware of things at 4:30 PM than they are at 6 in the morning, you can forget the solstice as the official “shortest day of the year” in terms of daylight.
For example, in Boston, the Sun starts setting at 4:11 p.m. on December 5, and won’t start setting later, at 4:12 p.m., until December 13.
Of course, the degree of darkness varies, depending on how far north you live and, as for the time the clock reads at sunset—this also depends on how far east or west your home sits, relative to your standard time zone.
For northern latitudes, the earliest sunsets of the year happen around December 7 but, if you live about 25 or 26 degrees N. latitude, your earliest sunsets are actually in late November.
Drive just an hour east from where you are right now, and the Sun sets ten minutes earlier, and that’s because going east around the Earth’s curve makes your western horizon rise up to block the Sun sooner.
The exact date of earliest sunset varies with latitude. But the sequence is always the same.
And what about your sunset time?
Test this out yourself, and see when your sun starts setting.
Try watching two days ago, and then today, and one week from now.
And, in conclusion, why is the earliest sunset well before the winter solstice?
This is because of a discrepancy between our modern-day timekeeping methods and how time is measured using the Sun known as the equation of time.
Just to be clear, tropical sunsets hardly vary throughout the year, while polar sunsets like to change through the seasons.
Basically, If you lived right smack on the equator, for example in Quito, Ecuador, your minutes of daylight would never budge throughout the year, not even by one second.
By contrast, countries like Canada and Alaska experience the most radically short days in December.
But wherever you live, before winter starts, your afternoons will start getting brighter!
Images from web – Google Research