Today Is Winter Solstice, But Sun Began Setting Later Several Days Ago. Here's Why

At 3:55 p.m. Saturday, the sun was already close to
setting over St. Albans, Vermont. Today is the winter
solstice, the shortest daylight of the year. But 
strangely, sunsets started getting a bit later
starting December 10. There's a reason for that. 

The winter solstice hits today at 10:03 a.m. 

It is the shortest daylight of the year, but even, the earliest sunset and latest sunrise of the season don't exactly line up.  

Believe it or not, our earliest sunset was about a week and a half ago. And our latest sunrise won't hit until just before the New Year arrives.  

Why?

It's a little complicated, but here it goes: 

As Timeanddate.com explains:

"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."

The equation of time is the difference between time measured using a sundial, also as true or apparent solar time, and the time measured using a clock, also known as mean solar time.....

Most clocks run on the idea that a day is exactly 24 hours. Technically a day is the duration between one solar noon, the time of day the the sun is at the highest point in the sky, to the next."

A solar day is not exactly 24 hours long. It varies through the year because the elliptical shape of Earth's orbit and the tilt of our planet. A solar day is longer than 24 hours in the summer and winter solstice. It's a little shorter than 24 hours at the spring and autumn equinoxes. 

This means solar noon comes at a different time than the noon you see on your watch or smart phone. For instance, in New York City, solar noon hits at 11:54 a.m. clock time.  By January 3, the Big Apple's solar noon and "watch" noon both hit at 12 on the dot. On January 4, solar noon as at 12:01 p.m., and it keeps getting later through January, as Timeanddate.com explains. 

That shift in solar noon means both sunset and sunrise keep getting later into the first days of January. 

In Burlington, Vermont, the earliest sunsets of the year hit on December 8 and 9, at 4:12 p.m. With both sunrises and sunsets getting later, today is the shortest day of the year with a sunrise at 7:26 a.m. and sunset at 4:16 p.m.

Our sunrises will keep getting later for awhile yet. The latest sunrises are at 7:29 a.m. each day between December 30 and January 5. After that, sunrises start getting earlier while sunsets keep getting later. 

Basically. days get longer from now until January only very slowly. Once we get into January, the pace of lengthening days begins to pick up. 

COLDER TIMES AHEAD?

There's an old saying that as the days lengthen, the cold strengthens. 

And it's true: On average, the coldest weather of the winter comes around the third week in January. Every winter is different, of course, so the most frigid days in some years can come in December or February instead. 

But, the depths of winter are generally in the second half of January. 

Even though the northern hemisphere begins to get a little brighter after today, the high Arctic remains deep in darkness. What little warmth might be left up there radiates out into space. The supply of gelid air keeps growing, just waiting for a chance to rush southward onto poor unsuspecting people like us Vermonters.   

Meanwhile, lakes in southern Ontario and Quebec continue to freeze up. Parts of the Great Lakes do, too. That means Arctic air coming from the North Pole can't as easily absorb a bit of the warmth of the lakes to modify those pushes of frigid air. 

Also, as the lakes freeze, they're less able to transfer moisture to the air. That means fewer clouds downstream from the lakes here in Vermont. Nights are a little more likely to be clear in January than they were in November and December. Clear, calm nights tend to be the coldest. A clear January night a mean the bottom falls out of the thermometer. 

Though the days will slowly lengthen over the coming weeks, you probably won't get much of a break from our cold winter winds. 

But slowly, you'll eventually notice a change. Maybe on a February day, the winter sun will actually feel a little warm. As we get through the late winter, thaws start to become a little more frequent. Before you know it. balmy spring breezes will ruffle your hair and brighten your mood.  

Glimmer Of Hope: Earliest Sunset Comes Before The Winter Solstice

The earliest sunsets of the year and the latest sunrises
of the year by latitude. Source: EarthSky.org

 Every day since December 3, the sunset has been at 4:13 p.m. at least as measured in Burlington, Vermont.

That's the earliest sunset of the year. 

Today, December 16, the sun sets at 4:14 p.m. one minute later than it's been for the past couple of weeks or so. 

How can that be? Especially since the winter solstice - definitely considered to have the shortest daylight of the year -doesn't come until Thursday, December 21. (10:27 EST local time to be exact).

As you'd expect, the answer is sort of complicated. 

I'll let EarthSky.org explain it:

"Basically, 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 solar noon to the next - rarely equals 24 hours exactly. 

Also, solar noon is simply called midday, because it refers to that instant when the sun reaches its highest point for the day. Thus, in the month of December, the time period from one solar noon to the next is actually half a minute longer than 24 hours, For example, in Philadelphia, Pennsylvania on December 7, the sun reaches its noontime position at 11:52 a.m. local standard time, Then, two weeks later - on the winter solstice - the sun will reach its noontime position around 11:58 a.m.. So that's six minutes later than on December 7."

In other words, the one minute later sunset tonight here in Vermont is something of an illusion. But one I will gladly embrace. 

Interestingly, the further south you go, the earlier the earliest sunset happens, if that makes any sense. 

For instance, around here, the earliest sunset of the season is around December. 10.  Head down to Key West, Florida, and the earliest sunset of the year hits around November 29.

Of course, there's a price to pay for the ever so slightly later sunsets starting today.  It also means later sunrises into early January. The sun in Burlington rose at 7:23 a.m. this morning.  The sunrise will continue to get later and later until December 30 - after the winter solstice - when the sun comes up at 7:29 a.m. 

The sun will keep coming up at 7:29 through January 5. After that, it will start going the other way. 

Of course, winter cold lags behind the lengthening days by about a month. "As the days lengthen, the cold strengthens," goes the saying.

On average, the coldest time of year is somewhere around January 21, but that varies greatly year to year. 

Even though the days are getting longer through the first three weeks of January, the sun angle is so low, and the sun is so weak, that the Northern Hemisphere continues to cool.

It's not until February that the increasing angle of the sun just begins to erode the winter chill.  

If you want something to look forward to, the latest sunset of the year in Burlington hits age 8:41 p.m. eastern daylight time. That latest of the year sunset goes from June 21 through July 2.