Is it me, or is the sun wobbling?

[ChrisGreaves]

I am a simple sort of guy, and I expect the days to shorten for another week, then they will lengthen. I believe that the earth is spinning on an axis, but is wobbling a bit.

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That said I do not understand why this web site tells me that sunrise will vary by 9+38=47 seconds tomorrow while sunset tomorrow will vary by only 11 seconds.

I could accept, I suppose, sunset varying by 47 and, even, say, 40 seconds; but not eleven.

I had always assumed that the sunrise times and sunset times moved in a stately procession with equal intervals towards (and then away from) each other.

(signed) "In the dark, as usual" of Bonavista.

[ChrisGreaves]

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Loungers in Carrington, UK have cause for worry.
Their times appear to be 53 seconds and 5 seconds for sunrise and sunset advancement.
Cheers, Chris

[HansV]

The earliest sunset at our latitude was around the 13th of December, while the last sunrise won't be until around the 30th of December.

Since we are just past the date of the earliest sunset, sunset times hardly vary from day to day. And since sunrise will become later for the next 16 days, it currently varies more from day to day. At the end of the month, this will be reversed.

It's different for other latitudes - see The earliest sunset comes before the winter solstice

[Graeme]

And there's a lot of Precession going on too!

https://en.wikipedia.org/wiki/Axial_precession

Graeme

[RonH]

Oslo is now a bit short of 'sun up' ... apart from the fact that its mostly blocked with cloud

Screenshot_20231215-083422_Chrome.jpg

[ChrisGreaves]

Thanks for the explanations and the link, both of which will take me some time to digest this (shorter) day.
I should acknowledge that there was/is always the possibility that my data source may contain errors, and that while I hinted at “wobble” and “precession” I had not, and still do not, consider that to be a factor in my conundrum.
Further: I did not realize that sunrise/sunset times were not symmetrical around the solstices. On Dec 31 this year (Bonavista) sunrise will be 07:54:52 AM and the next day Jan 1 sunrise will be at 07:54:50 AM. Then arrives earlier. Our earliest sunrise is around the end of the year, about ten days after the traditional date of solstice..
I see now that for all of my astronomical life I have been using a general definition of “solstice” rather than local (Bonavista) definitions of “sunrise solstice” and “sunset solstice”. As noted in the preceding paragraph, for Bonavista the sunrise solstice seems to be Dec31/Jan 1.
I didn’t want to get that complex, but that’s what happens; just when I think I know something, it turns out that I don’t know the whole story.


Hans>>> Since we are just past the date of the earliest sunset, sunset times hardly vary from day to day. And since sunrise will become later for the next 16 days, it currently varies more from day to day. At the end of the month, this will be reversed.

That said, I had fortuitously used a level of measurement that my Numerical Analysis professor might have been proud of. I was not concerned so much with the actual times of sunrise (and sunset) as much as the differences between consecutive sunrise (and sunset) times. And that is still a mystery to me.

Hans>>> It's different for other latitudes - see The earliest sunset comes before the winter solstice

Thanks Hans, this was a good link; I have read it twice, once before sunrise and once after sunrise, and can’t say I understand it all.
Why? 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 one solar noon to the next – rarely equals 24 hours exactly.
This doesn’t fully answer the question; it shoves the blame for one thing onto another. I know want to know WHY the actual day rarely equals 24 hours exactly. That may become clear as I re-re-read the article, but because it is addressing the sunrise-time, rather than the change-in-sunrise-time it can’t explain my (Bonavista) view of the rate of change (47 versus 11 seconds).

I think but can’t yet prove that those different rates of change are because the sunrise- and sunset-times do not peak on The Day of the Solstice. Those rates of change are brought about by the separate days of the sunrise-solstice and the sunset-solstice.
I note too that the article states that The next solstice in 2023 comes at 3:27 UTC on December 22, so perhaps I am all wrong about thinking of a sunrise- and a sunset-solstice.

Also, solar noon is simply called midday, because it refers to that instant when the sun reaches its highest point for the day This too seems to be a red herring, because again I am puzzled by the rate-of-change rather than the difference between any local mid-day time. I think.

Anyway, thanks for the article link. It is still a good one, if only because it has caused me to dig deeper than I might have done. And again I look back on my university days and regret that I was unable to ask my lecturers questions in case they thought I was stupid. Today I know the difference between stupidity and ignorance.
Cheers, Chris

[ChrisGreaves]

https://en.wikipedia.org/wiki/Axial_precession

Thanks Graeme. I was still playing with my spinning top after age ten, so i remember precession very well.
In general, though, I think of precession (solar, lunar, planetary etc) as being several orders of magnitude greater than a human lifetime, and because of that thought, do not see precession as a cause of day-by-day rates of change. as in "For identical reasons, the apparent position of the Sun relative to the backdrop of the stars at some seasonally fixed time slowly regresses a full 360° through all twelve traditional constellations of the zodiac, at the rate of about 50.3 seconds of arc per year, or 1 degree every 71.6 years."

The aricle seems good, and I shall study it in detail, but for now, I can not make the link between "precession" and change-of-sunrise time and change-of-sunset times is measurably different.

Once again I confess that my enquiry was poorly worded.

Cheers, Chris

[kdock]

the last sunrise won't be until around the 30th of December.

Hans!! Are you predicting the End of Days???? I sure hope it's sunny December 30th.

Kim

[HansV]

[Graeme]

and that while I hinted at “wobble” and “precession” I had not, and still do not, consider that to be a factor in my conundrum.

Perhaps a more specific answer to your conundrum would have been that the change in length of day is not linear because of Earth's elliptical orbit and because of the obliquity of the orbit. These two things together cause the sunrise and sunset time to vary by the missing 11 seconds!

https://www.redshift-live.com/en/magazi ... ays-1.html

Graeme

[ChrisGreaves]

I am still wading through the explanations, and find that most of them will boil down to geometric/topological maths. That is, I will have to do some work in order fully to understand what is going on. For me it is not enough to know that "the entire system wobbles".

In the meantime this morning's news brings On which days does the Sun rise the earliest and set the latest? which brings us "Despite the summer solstice marking the longest stretch of daylight over a 24-hour period, it is not the day when the Sun rises the earliest or sets the latest. The earliest sunrise and the latest sunset fall about a month apart"
It seems that we all have two solstices to celebrate this winter (and next summer); the sunrise solstice and the sunset solstice, in terms of time-of-day relative to local standard time of mid-day.
Cheers, Chris

[BobH]

Yabbut, tomorrow days begin to get longer in the northern hemisphere.