Northern hemisphere dwellers: we have just had the earliest sunset of the year, on December 7.

[mahatmakanejeeves]

This is science, people. In another month, we won't be getting much more of that.

I'll drag out my "equation of time" links. This is a fascinating subject.

We have just had the earliest sunset of the year, on December 7.

If you live in the northern hemisphere, the sunsets will be occurring later each day from now until June. The day on which the earliest sunset occurs is not the day with the least amount of sunlight. It is also not the day on which the latest sunrise occurs.

Earliest sunset at 40 degrees N. latitude on December 7

The exact date for the earliest sunset or earliest sunrise varies by latitude. Toward the end of the first week of December, mid-temperate latitudes in the Northern Hemisphere have their earliest sunsets. The earliest sunset for 40 degrees N. latitude is on December 7. That would be the latitude of New York City (shown in Jerry Ferguson‘s photo, top of post); Philadelphia, Pennsylvania ; Kansas City, Missouri; Reno, Nevada; Beijing, China; Madrid, Spain; Naples, Italy. Meanwhile, the Southern Hemisphere’s mid-temperate latitudes are waking up to their earliest sunrises.
....

It seems paradoxical. At middle latitudes in the U.S. – and throughout the Northern Hemisphere – the earliest sunsets of the year come about two weeks before the solstice and the shortest day of the year.

Why isn't the earliest sunset on the year’s shortest day? It's because of the discrepancy between the clock and the sun. A clock ticks off exactly 24 hours from one noon to the next. But an actual day - as measured by the spin of the Earth, from what is called one “solar noon” to the next - rarely equals 24 hours exactly.

Solar noon is also called simply midday. It refers to that instant when the sun reaches its highest point for the day. In the month of December, the time period from one solar noon to the next is actually half a minute longer than 24 hours. On December 7, the sun reaches its noontime position at 11:52 a.m. local standard time. Two weeks later - on the winter solstice - the sun will reach its noontime position around 11:59 a.m. That's 7 minutes later than on December 7.

The later clock time for solar noon also means a later clock time for sunrise and sunset.

Sunrise and Sunset, Washington, DC

You can look at the times for any month you choose.

Bonus link:

Why doesn't the earliest sunset occur on the shortest day of the year?

[liberal N proud]

1. And I always assumed that happened on the winter solstice.

Learn something new all the time.

[mahatmakanejeeves]

2. Also, the latest sunrise is in January. Check a local almanac.

Last edited Thu Dec 8, 2016, 11:42 PM - Edit history (1)

You will be able to notice by Christmas that the sunsets are getting later.

[Pacifist Patriot]

3. Me too. Our family has a dinner table ritual...

where we all share something we learned during the day. I got mine for tonight!

[PearliePoo2]

4. I love stuff like this. I looked up my location and

the sunset changes on the 13th, so a few more days to go. But it is still better than the 21st like I always assumed!
Thanks!
Edited to add my latitude is: 48.5343° N

[elleng]

5. GOOD!

Last year I followed this (more carefully,) but other damn things have intruded this year.

According to my 'local' weather.com, today's sunset here occurs @ 4:45 p.m. and the sky will be clear, so I'll get pics!

Solar noon @ 11:59 'a.m.'

[mahatmakanejeeves]

7. A long explanation from eleven years ago.

My favorite astronomical effect.

Just about everyone knows that, in the northern hemisphere, the day with the least amount of daylight marks the winter solstice, which occurs on or about December 21. It is not, however, the day with the earliest sunset or the latest sunrise. The earliest sunset occurs on December 7, or, as it did in 2003, December 8.

Years ago, wondering why this was so, I called the Naval Observatory in DC. Someone there explained the reason for this to me. Basically the cause is that, because the earth is at perihelion in January, it is moving faster in its orbit than it is at aphelion, which occurs in July. It is related to something called the "Equation of Time."

Not many people know about the effect, so, when my mom, back in 2003, said she had seen something about it in the paper, I just had to find it.

Forecast: Sunnier Days Ahead

Sunday, December 7, 2003; Page B06

Buck up! Despite this weekend's wintry weather, there is hope.

Many people know that the start of winter and shortest day of the year is the winter solstice, usually Dec. 21 (it slips a day some years). Not widely recognized is that even though the 21st has the shortest day, it does not have the earliest sunset. The earliest sunset of the year is tomorrow, Dec. 8.

From here on out the afternoons get longer, and we can begin to revel in additional, growing light to guide our homeward commutes. This quirk results because the latest sunrise on the calendar is about Jan. 4, but the earliest sunset is about Dec. 8. The winter solstice of Dec. 21 is midway between these two dates.

So, no need to wait for Dec. 21 to herald the start of "longer" days.

GEORGE BROWN
Washington

The effect is illustrated at Equation of Time, but it helps to have someone sit down and go through a slow explanation of how, because of the Earth's motion along its orbit and its proximity to the Sun now, it has to turn a little more than 360 degrees from one day to the next so that the Sun is directly overhead at noon. If you compare noon as indicated by a sundial to noon as indicated by a clock, you will notice the disparity.

Every website shows or has a link to the chart that shows the daily discrepancy, but I can't find a site that really explains the effect simply, which is, believe it or not, easy to do.

It doesn't seem possible, but watchmakers have, for centuries, made watches that can compensate for the difference.

Mouvement d'horlogerie à quantième perpétuel comportant un mécanisme à équation de temps avec affichage

You won't see this at Walmart.

If you haven't had enough, Google "equation of time", or ask any astronomer. If you bring this up in science class, people may think you are smart.

The dean of the DC-area weather forecasters, Bob Ryan, from Buffalo, New York, puts out an almanac every year. Let's look at some times for sunsets and sunrises from his almanac. On November 30, 2005, the sun set at 4:47 p.m. On December 1, the sun set at 4:45 p.m. The sunset remains at 4:45 p.m all the way through December 12. On the 13th, the sun sets at 4:47 p.m again. That makes December 7 or so the day with the earliest sunset.

Meanwhile, the sunrise is getting later every day. On December 1, the sun rose at 7:07 a.m. On December 7, sunrise is at 7:13 a.m., and on December 13, sunrise is at 7:17 a.m. The sun rises at 7:27 a.m. from December 31 all the way through January 10. Split the difference to get the day with the latest sunrise as January 4 or January 5.

DC is at about 39 degrees north latitude.

This really is the best time of year. The sunsets are beautiful, and in the southeastern US, the dreadful humidity and mosquitos are blissfully gone. DC never looks handsomer than it does in December. All the museums and other buildings, like the Willard Hotel, are full of poinsettias and displays. I must get down to the Botanical Gardens.

By the way, my watch has stopped. Does anyone know what time it is?

[elleng]

8. After sunset, today!

[Warpy]

9. I'm fairly far south here in NM

which means it's not nearly as grim as Boston was this time of year. However, twitlight at 4:45 in the afternoon SUCKS.

The combination of dark days and "standard" time are a double whammy this time of year. It feels like living deep in a cave, daylight visible dimly and far away.