Why after the shortest day does the sun continue to rise later for several days although it sets later.?

Answer 1

Hi Charly!

The winter solstice (December 22 this year) is the shortest day of the year, but it is not the earliest sunset, nor the latest sunrise.

Lots of people think that the earliest sunset, the latest sunrise and the shortest day are all on the same day, the winter solstice, but in reality each falls on a different day.

For most of the year, the apparent northward and southward motion of the sun governs the changing times of sunrise and sunset. When the sun is moving southward, as it is in September, days in the Northern Hemisphere grow shorter.

The path of the sun across the dome of the sky is known to trigonometry buffs as a "sine curve." In September, when the sun is moving southward at maximum speed, the days grow shorter by over 3 minutes per day. In December, however, the sun "levels off". The southward motion slows and comes to a stop. For about a week, the sun appears to stand still above the Tropic of Capricorn. The shortening of the day's length slows and stops on December 22 (in 2007).

The north-south motion is not the only one, however. Two others are at work, and together they are known as the "Equation of Time.".

One is based on a simple principle of geometry.

Look at the “sine curve” again. The northward/southward component is only a small part of the sun’s daily motion. Mostly, the sun is moving eastward day by day. In December, the sun is moving almost purely eastward. In September, however, a helping of southward is mixed in with the eastward motion.

Think about that. If the sun covers about the same distance in the sky each day, it’s going to make better eastward time in December, when it’s moving purely eastward, than in September when some of its motion is devoted to moving south too. But to our clocks, each day is exactly the same length, 24 hours, the sun’s average time. This means that, since the sun is moving eastward more in December than September, the earth must spin a little longer to catch up with the sun’s farther-than-average eastward motion. In December, it takes about 20 extra seconds of rotation for the earth to catch up, compared to the time it would take in September.

Now, notice what happens to the time of sunset each day.
As the shortening of the days finally damps out in early December, the sunset is no longer getting much earlier each afternoon. But the sun is still both rising and setting about 20 seconds later each day than the day before because of the sun's greater-than-average eastward motion. The point is reached, in about the second week of December in north temperate latitudes, where that 20 seconds a day starts to exceed the fading shortening of the day. When that happens, the sunset slowly reverses and begins to come later, even though the solstice is still almost two weeks away.

In the morning, now, the opposite is happening. Through December, the sunrise is still moving later and later each morning, both because of the shortening day and also the extra 20 seconds needed to catch up with the sun’s maximum eastward motion. The shortening stops in time for the solstice, December 22nd, but because of the extra 20 seconds a day, the sunrise continues to move later, even after the solstice. In fact, it skids all the way into the first week of January until the lengthening of days after the solstice finally begins to drown out the extra 20 seconds a day. That’s why the latest sunrise is in the first week of January in north temperate latitudes.

A similar thing happens in June, because in June the sun is also covering more eastward territory each day than at other times. The effect in December is more pronounced than the one in June, however, due to the earth’s elliptical orbit.

In December and January, the earth is moving faster in its orbit than at any other time of the year. This makes the sun appear to move farther each day than at any other season, about 10 seconds further than average. Much the same as with the 20 seconds-per-day, this delays both the sunrise and sunset in December and January, making the earliest sunset here in New York December 8, and the latest sunrise January 4th, about 27 days apart.

In June, however, the earliest sunrise comes on June 15th, while latest sunset is June 27th, only 12 days apart. This is because in June and July, the earth is moving the slowest in its orbit. The difference between the 27 days in December-January and and the 12 days in June is caused by the contrast between the earth’s speed in December and June.

If you were in England, your latest sunrise would come at the end of December, not in early January as mine does. That's because the effect is less pronounced farther from the equator because the northward-southward difference in day's length is greater as you approach the polar regions. The day's length goes from zero to 24 at the Arctic and Antarctic Circles, but at the equator it never varies from 12.

So you have discovered, although the sun is now past the solstice and the days are no longer getting shorter, the sun will continue rising later each morning, for a week in Britain and for almost two weeks here in the United States.

P.S. to Philip! I'll accept your "treatise" quip as a compliment! Anytime I answer a question here, my prime objective is to help the asker to understand. I don't see any value in one-liners, especially for a complicated subject the Equation of Time, or in simply cutting and pasting lengthy text (which the lifter probably doesn't understand himself).

If Philip's adumbrated version were sufficient to answer the question, perhaps he would then explain why the same phenomenon happens in June, even though the earth is at that time moving slower than at any other. One would expect the phenomenon in June to be the reverse of December, when in fact they are both the same.

To Charly, Philip and all other readers, ask yourself this question: After reading my answer, did you gain a better understanding? If you do, I have succeeded!

Answer 2

This is a lovely question and far more complicated to answer than you might imagine. I really don't have the time to explain it fully, there are excellent websites that will do that for you but I will give you a taste.

The earth revolves about its axis and orbits the sun. Solar noon is when the sun is directly overhead at any spot. The time between two consecutive solar noons is a solar day. Solar days are not the same length throughout the year. They are shortest at the equinoces and longest at the solstices.

If solar noon is getting later and later on clock time approaching the solstice, then sunset is also getting later. This means that by the time the solstice arrives, the ealiest sunrise has already occurred, some three weeks beforehand.

As I said, this is only a taste and it gets quite complicated. Remember, if the earth is revolving on its axis while orbiting the sun, there is a complete extra revolution to be accounted for somewhere along the line - and that comes into it as well.

Believe me, it is worth Googling for this. The complete answer takes some application of logic and thought - and two or three pages - but it is immensely satisfying once you start understanding it.

Answer 3

Astute of you to notice this. It is because the Earth is moving through space in its orbit, and that changes the apparent position of the Sun. Try to imagine what would happen if the Earth was to stop rotating. The Sun would not stop in its place in the sky, but would instead seem to move very slowly backward. This apparent eastward shift resulting from the Earths motion through space is why it takes a little extra time in the mornings to get sunrise. Now that the Solstice has occurred, the apparent northward motion of the Sun will overcome this effect (usually in early January), and the sunrises will become earlier.

Answer 4

The earth is tilted at a relentless volume (ecliptic) as you're saying yet advances in its orbit a pair of million/365 of the circumference consistent with day. This differences the area of the shadow of the solar on earth's floor much less calmly (sundown and daybreak) than if the earth remained in place in its orbit and only spun on its axis. on the shortest day on the 'exchange factor' the lean is strictly far off from the solar interior the norther hemisphere (yet in direction of the solar interior the southern hemisphere the place the discrepancy you point out could desire to be reversed). whether, the internet length of day grows longer each and every day after the solstice. The action of the earth around the solar is likewise no longer as uniform as a factor on a rotating stable wheel and daybreak/sundown additionally rely on the place on earth you word them (far-north/equator/far-south, etc.). by the way, the coldest climate usually follows the shortest day because of the fact climate varieties have their very own momentum that could desire to be reversed in wintry climate (or in summer following the longest day).

Answer 5

I think I saw the correct answer hidden in the middle of that treatise by AnnMarie, but just in case you missed it, I'll say it more concisely.

The Earth's elliptical orbit brings us closer to the sun in December, so we are moving around the sun faster. Since both Earth's daily rotation and its orbit around the sun are in the same direction, we have to rotate a little farther each day in winter to catch up with the sunrise, which seems to be retreating from us faster in winter than in summer.

Answer 6

I would have loved to answer this question but cyswxman managed to beat me on the mark. I can only but praise his words and ... give him a thumb up! :-)