The earliest sunset
[NOTE: This is a slightly edited repeat of an earlier post.]
The earliest sunset is not at the solstice, the shortest day of the year. It comes somewhat earlier (now, for example), and varies slightly depending on latitude. Here’s an explanation for the phenomenon:
The key to understanding the earliest sunset is not to focus on the time of sunset or sunrise. The key is to focus on what is called true solar noon – the time of day that the sun reaches its highest point, in its journey across your sky.
In early December, true solar noon comes nearly 10 minutes earlier by the clock than it does at the solstice around December 21. With true noon coming later on the solstice, so will the sunrise and sunset times…
The discrepancy occurs primarily because of the tilt of the Earth’s axis. A secondary but another contributing factor to this discrepancy between clock noon and sun noon comes from the Earth’s elliptical – oblong – orbit around the sun.
Read the whole thing.
For me, the earliest sunset days are the darkest days, because I’m not an “up with the lark” person. And the reversal to longer days (that is, to later sunsets) starts very soon where I live, which makes me happy.
The gloom here is so depressing this time of year. It gets daylight at a little before 8 and then sunset is about 4:10 but when you factor in the gloomy cloud cover it is more like 8:15 to 3:30.
Make up for it in summer but it’s no fun in December.
I was fascinated to learn years ago that the latest sunrise where I live comes on a day well after the solstice. This year it is at 7:14AM on January 8. Note that the day length that day is 9:09:59, it is 8:58:02 on the solstice.
Where I live we get it two ways: Boise is at the 43rd parallel and at the far west end of the Mountain Time Zone (in fact we’re further west than Las Vegas, which is in the Pacific Time Zone). So today the sun will rise at about 8:10 AM, and go down at 5:07. By the end of the month the sunset will already be noticeably later.
So glad I’m out of New England and closer to the equator. The difference in daylight hours, even in northern Florida compared to what I experienced in December in CT is amazing.
Part of the problem is that New England is at the extreme eastern edge of the time zone which exacerbates the sunset time. A solution which has been proposed but never seems to go anywhere is to move NE to the Atlantic time zone.
But if NE was moved to the Atlantic time zone then it would get insanely late sunrises in the winter, before the time changes in October, and after the time changes in March. Having been in school during the winter of 1974 when the country went on permanent DST due to the supposed energy crisis, it was not fun when the sunrise in early January was at 8:14.
One thing I enjoy about living in the Bay Area as opposed to my MA origins is that, along with the milder weather, the early winter sunsets are not nearly so extremely early, given that we’re fairly west within our time zone. Sunset now is at 4:49, as opposed to 4:12 in Boston. And given that we’re a decent way south our sunrises are only ten minutes later.
Marisa,
Try living in China. It geographically spans 5 time zones but the whole country follows one time zone, “Beijing Time.”
physicsguy,
And, as you know, it’s not the amount of hours of sunlight as much as the angle of the sun in the sky, or, more correctly, the amount of atmosphere the sun’s rays (and photons) have to travel through before they reach your eyes and skin (although the extra time is nice also). I remember being shocked by how much of a difference it made in my mood and energy level when I moved to Florida from the upper midwest.
Five time zones in one country? That’s carrying communism way too far — no surprise, I guess.
India covers two time zones and compromises by setting its time at the half-hour in between the two. So when we lived there we were 10.5 hours ahead of the eastern US.
Went to Edinburgh Scotland on a New Years trip while in England, seemed to be barely 6 hours of daylight
We should all just live on or near the equator. It simplifies everything greatly. It’s either very wet and hot or humid and hot. Sun is either up or down. No shillyshallying about it.
I’ve said this before, and it’s no insult to anyone, there are plenty of basic, fundamental things necessary for life on Earth that I am clueless on (how to grow food and hunt, for example), but I’ll bet less than 5% of people on Earth know it’s the Earth’s tilt on its axis that gives us non-equatorial dwellers seasonal changes. The most common answer I get when I ask folks is: distance from the Sun. It’s not true, but that at least implies they know the Earth’s orbit about the Sun is an ellipse and not a circle. And it implies they know the Earth orbits the Sun, which is also a good sign.
The fun thing with true solar noon is that if you try to match your local noon to it you don’t end up with a twenty-four hour day.
Clockmakers took to mean solar time as soon as they could make something precise enough.
Oligarchs probably know more about the Analemma than the rest of us:
https://quillandpad.com/2021/05/09/equation-of-time-eot-what-is-it-and-whats-the-attraction/
EOT complications are a big thing in haute horlogerie.
http://www.danielslondon.com/daniels-watches/the-space-traveller/
I remember when I discovered this unusual disconnect between earliest sunset/shortest day. First I went to the almanac to try to make sense of it, but that was just timetables. It took a little research to understand it fully, thanks for sharing this with everybody. Darn celestial mechanics!
Weird how the days pass differently too. I remember the first time I worked on the equator was in high summer – I had come from growing up in the north where it was light until almost midnight. On the equator, you can count the twilight in minutes. It’s more, lights on, lights off. Took some getting used to.
Daniel Boorstin’s, “The Discoverers” includes a wonderful account of man’s history attempting to divide the day into regular intervals and build devices to accurately measure those intervals. He also gives a great account of the chase to capture the huge cash reward of the Longitude Prize: https://www.arcgis.com/apps/MapJournal/index.html?appid=924e838ba3734e0b9b928a3610b24a87
Griffin —
No kidding about the gloom. I’ve been knocking off work early at 3:30* to go for my walk and half the time the streetlights are already on when I start.
* (I check in when I get back, promise! Okay, not really. The rest of my team is on the East Coast, so they’re long gone already.)
Rufus:
If you look at a time zone map you can see all kinds of anomalies. E.g., France and Spain are mostly the same longitude as the British Isles but is on the same time zone as the rest of Western Europe. Ergo, it’s effectively on DST for 1/3 of the year and double DST for 2/3.