Loooooong story.... I'll cut and paste from an existing one. This is twelve years old, but it still works.
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 for "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, used to put 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?
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http://forums.insidelacrosse.com/threads/my-favorite-astronomical-effect.32746/#post-940134
It's that time again.
I love this picture. Suppose you set up a camera on a tripod aimed at the east-southeast and that once per week, at the same time of the morning, you took a picture of the sun fairly low in the sky. At the end of the year, you put all those images on top of each other. This is what that composite image would look like.
Time lapse photograph of the sun taken at 8:30 a.m. over a one-year period.
Right now, the sun is nearing the low point of this lopsided figure 8, which is called an analemma. The point where the path crosses itself marks the position of the sun on March 15 and September 1.
In other news, Mercury rises about 5:30 a.m. in the DC area these days. It is easily visible at 6 a.m., even in the middle of a city.
This will be on the exam.
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http://forums.insidelacrosse.com/threads/my-favorite-astronomical-effect.32746/#post-940225
So the shortest day of the year is not on the day that the sun sets the earliest?
That's right. Not many people know it, either. Every morning, however, the newspaper prints the sunrise and sunset for that day, so the numbers are there to see. It took me years to learn what the deal was.
The ancients spent a lot of time studying the skies, and they were aware of anomalies to the sun's motion.
The earliest sunset of the year will be just about a week now, at 4:45 p.m. in DC. As we are at the winter solstice, the sun will "stall" in the sky, and it will set at about the same time for the first twelve days in December. By the time the shortest day comes around, the sun will already be setting later.
Meanwhile, the sun will continue to rise later until the first week in January. Then, it changes course and begins to rise earlier. You're at about 46 or so degrees north latitude, so the numbers are different for you than they are for me.
Wikipedia, Equation of Time
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Related subject: the analemma.
Happy Bottom of the Analemma Day everybody.
http://en.wikipedia.org/wiki/Analemma
= new reply since forum marked as read
