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Scooot

Winter Solstice Curiosity

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Our days get shorter as we approach the winter solstice (22/12/19) and longer thereafter as the sun gets higher.

At my location, using Sky Safari.

21/12/19 Dawn 7:21:22 Dusk 16:30:58 day length 9:9:36

22/12/19 Dawn 7:21:53 Dusk 16:31:28 day length 9:9:35

23/12/19 Dawn 7:22:21 Dusk 16:32:01 day length 9:9:40

I was surprised to find it was 1 second shorter from the 21st to 22nd but then 5 seconds longer from the 22nd to 23rd. Presumably the difference in shortening and lengthening is due to my location but I wonder where this difference is the same & why. :) 

 

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Is it something to do with the fact that the actual moment of the Solstice is embedded somewhere within the hours of one of the days you have listed,  and not nicely at Noon or mid-night . 

Hence the daylight  lengths will have an unequal contribution of daylight duration from  a): the Sun moving towards Solstice..... daylight shorter.......   and b):   the Sun moving away from Solstice....daylight longer.  eg. If the Solstice is towards Midnight then the following day may have a similarly short daylight day due to the skewed timing....

...errr.. I think I understand myself.... just a guess though.

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2 hours ago, Craney said:

Is it something to do with the fact that the actual moment of the Solstice is embedded somewhere within the hours of one of the days you have listed,  and not nicely at Noon or mid-night . 

Hence the daylight  lengths will have an unequal contribution of daylight duration from  a): the Sun moving towards Solstice..... daylight shorter.......   and b):   the Sun moving away from Solstice....daylight longer.  eg. If the Solstice is towards Midnight then the following day may have a similarly short daylight day due to the skewed timing....

...errr.. I think I understand myself.... just a guess though.

Thanks but I don’t think so. I had the time set at mid-day but the figures I used were civil dusk & dawn from the description. See below. They’re the same regardless of what time I read it.

15A6B76E-BDB4-4766-80A0-216CFF075BC8.thumb.png.5d63cff4515574445e6e428cb5db9ce6.png

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4 hours ago, Craney said:

Is it something to do with the fact that the actual moment of the Solstice is embedded somewhere within the hours of one of the days you have listed,  and not nicely at Noon or mid-night . 

Hence the daylight  lengths will have an unequal contribution of daylight duration from  a): the Sun moving towards Solstice..... daylight shorter.......   and b):   the Sun moving away from Solstice....daylight longer.  eg. If the Solstice is towards Midnight then the following day may have a similarly short daylight day due to the skewed timing....

...errr.. I think I understand myself.... just a guess though.

The soltice occurs at 0419 gmt on the 22nd in the UK.

The shortest day being 7hours 49mins and 43 seconds long.

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1 minute ago, wxsatuser said:

The soltice occurs at 0419 gmt on the 22nd in the UK.

The shortest day being 7hours 49mins and 43 seconds long.

Ok thanks Mike, I should have used sun rise and set times. 
It’s still the same though, 21st to 22nd is 1 a second shorter day but 22nd to 23rd is a 6 second longer day.

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Isn't that the answer then? It's shorter until solstice and then longer. 

 

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1 hour ago, skybadger said:

Isn't that the answer then? It's shorter until solstice and then longer. 

 

Yes but I was wondering why it wasn’t the same. If it’s 1 second shorter from the 21st to the 22nd why isn’t it 1 second longer from the 22nd to the 23rd. It’s not, the day is 6 seconds longer on the 23rd.

Edited by Scooot

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17 hours ago, Craney said:

Is it something to do with the fact that the actual moment of the Solstice is embedded somewhere within the hours of one of the days you have listed,  and not nicely at Noon or mid-night . 

 

 

12 hours ago, wxsatuser said:

The soltice occurs at 0419 gmt on the 22nd in the UK.

 

10 hours ago, Scooot said:

Yes but I was wondering why it wasn’t the same. If it’s 1 second shorter from the 21st to the 22nd why isn’t it 1 second longer from the 22nd to the 23rd. It’s not, the day is 6 seconds longer on the 23rd.

 

If  you were to go to a place on earth on the 22nd where local noon is at 0419 GMT then the length of the 21st and 23rd would be about the same (with the 22nd a tad shorter).

If  you were to go to a place on earth on the 22nd where local mid-night is at 0419 GMT then the length of the 21st and the 22nd would be about the same.

If the sun were a better time-keeper then these compared day lengths would be exactly the same. The sun speeds up and slows down at times on its apparent journey along the ecliptic which obviously feeds into the measured length of day.

If the solstice were to fall on the 22nd at local-midnight when the earth is at aphelion (or perihelion) then the lengths of the preceding and following days will be virtually the same.

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1 hour ago, Tiki said:

 

 

 

If  you were to go to a place on earth on the 22nd where local noon is at 0419 GMT then the length of the 21st and 23rd would be about the same (with the 22nd a tad shorter).

If  you were to go to a place on earth on the 22nd where local mid-night is at 0419 GMT then the length of the 21st and the 22nd would be about the same.

If the sun were a better time-keeper then these compared day lengths would be exactly the same. The sun speeds up and slows down at times on its apparent journey along the ecliptic which obviously feeds into the measured length of day.

If the solstice were to fall on the 22nd at local-midnight when the earth is at aphelion (or perihelion) then the lengths of the preceding and following days will be virtually the same.

Ah many thanks. I think I understand. A bit like Craney said after all, :) , my apologies for not understanding you @Craney

Edited by Scooot

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4 hours ago, Tiki said:

If  you were to go to a place on earth on the 22nd where local noon is at 0419 GMT then the length of the 21st and 23rd would be about the same (with the 22nd a tad shorter).

If  you were to go to a place on earth on the 22nd where local mid-night is at 0419 GMT then the length of the 21st and the 22nd would be about the same.

If the sun were a better time-keeper then these compared day lengths would be exactly the same. The sun speeds up and slows down at times on its apparent journey along the ecliptic which obviously feeds into the measured length of day.

If the solstice were to fall on the 22nd at local-midnight when the earth is at aphelion (or perihelion) then the lengths of the preceding and following days will be virtually the same.

It's not the Sun's fault as such but our orbit and all the other objects in the solar system.

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The difference in sunrise and sunset times often confuses people. Already the nights are getting lighter but the mornings are still getting darker...

The Earth rotates at the same speed but moves along its orbit at varying speeds due to eccentricity. This causes a bit of lag as the earth moves along its orbit (this time of year) quicker than it rotates. Our clocks are too accurate to cope with this.

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I always used to tell my students that the days were shorter in the Northern hemisphere during Winter because of the cold🤔.

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I think that the analemma explains the discrepancy nicely:

 https://starinastar.com/stellarium-see-analemma/

http://www.sciquill.com/analemma/page2.html

First time I saw an analema image I couldn't work out what it was telling me. Once you get your head round it there is a wealth of interesting information to be seen. 

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1 hour ago, Paul M said:

I think that the analemma explains the discrepancy nicely:

 https://starinastar.com/stellarium-see-analemma/

http://www.sciquill.com/analemma/page2.html

First time I saw an analema image I couldn't work out what it was telling me. Once you get your head round it there is a wealth of interesting information to be seen. 

Thanks very much for posting this. It’s very interesting. I will have to watch it & read it a few more times for it all to sink in. :) 

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This graphic provides a reasonable visualization as to what is going on.

 

1971254022_EquationofTimeandAnalemma1.gif.644bb11368676bbbbef29ea79f52aae7.gif

K

 

 

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