Nights drawing out again

[pawl]

Shortest day(Winter Soltice) is the 21 of December.

 

[Beebo]

Shortest day(Winter Soltice) is the 21 of December.

Correct, but the latest sunrise and earliest sunset are not on the same day, and neither of them are on the 21st.
That is just the day when the difference between the two is the shortest.

 

[nickyboy]

Still getting smaller til the 21st.

I understand the principle that "true" midday isn't at 1200. But why does the rate of change in the sunrise time differ from the rate of change in the sunset time?

 

[Beebo]

I understand the principle that "true" midday isn't at 1200. But why does the rate of change in the sunrise time differ from the rate of change in the sunset time?

Probably something to do with the shape of earth and shape of orbit, neither of which are perfect circles.

 

[si_c]

Probably something to do with the shape of earth and shape of orbit, neither of which are perfect circles.

It's also related to the relative axis of the earth to the sun, nothing quite lines up. If you think of the nuclear logo, and the path the electrons take around the core, like that our orbit around the sun is not flat, and with the tilt of the earth remaining stable as it moves around, our simplistic view of mid-day is inevitably wrong.

It's one of those things that is difficult to grasp in the abstract, but makes sense when you see it.

In fact the movement of the earth is more complicated than that, and if you also consider the movement of the sun, rather than being elliptical, the path of the planets are spiral.

 

[marinyork]

I understand the principle that "true" midday isn't at 1200. But why does the rate of change in the sunrise time differ from the rate of change in the sunset time?

Look up what an analemma is, this is a visual explanation of other factors (like time of day, shape of orbits, earth having a tilt, latitude etc). It's not that an equation of time explanation is wrong, it's that you can visualise what the heck we're on about here.

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

N.B. to be clear, the explanation of the perihelion (earth being closest to the sun in January) is not lined up with the solstice is essentially the same thing.

Also Analemmas are not vertical when you move away from midday (excluding tilt). They become asymetrical figure of eights that are rotated from vertical. The latitude also matters.

 

[DaveReading]

Why Isn't the Year's Earliest Sunset on the Winter Solstice?

 

[classic33]

I say we go back to using sundials.

 

[marinyork]

Actually I wasn't happy with the point about analemmas so let's go extraterrestrial!

Analemmas. People might ask well why a figure of eight, why not a dot, a circle, an ellipse or a teardrop?

http://www.analemma.com/pages/otheranalemmas/otheranalemmas.html

 

[nickyboy]

Look up what an analemma is, this is a visual explanation of other factors (like time of day, shape of orbits, earth having a tilt, latitude etc). It's not that an equation of time explanation is wrong, it's that you can visualise what the heck we're on about here.

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

N.B. to be clear, the explanation of the perihelion (earth being closest to the sun in January) is not lined up with the solstice is essentially the same thing.

Also Analemmas are not vertical when you move away from midday (excluding tilt). They become asymetrical figure of eights that are rotated from vertical. The latitude also matters.

OK, that makes sense now. I had previously assumed (without putting any thought into it) that any analemma would be a vertical line

 

[classic33]

OK, that makes sense now. I had previously assumed (without putting any thought into it) that any analemma would be a vertical line

You've put that much thought into it, you lost the 11 seconds from today.

 

[Globalti]

Winter solstice is the best time, I'll crack open a bottle of Moorhouses Blond Witch, dance naked on Pendle Hill and deflower a few virgins.

Then I'll wake up and have to leave home at 7:15 to park on the M66 for an hour.

 

[Slick]

[QUOTE 5082732, member: 9609"]our path round the sun is more egg shape than circular, at this time of year we are at the blunt end of that egg shape path and this causes a rapid shift in true mid day (half way between sun rise and sun set), it is the change in true midday that causes this anomaly. from memory true mid day (on zero long) shifts from about 11:45 to 12:15 from about mid nov to mid jan.

and it will be an utter miracle if anyone understands that explanation [/QUOTE]
No, I actually get it now which doesn't happen often.

 

[raleighnut]

For years now every time the Winter Solstice is mentioned I hear the first couple of lines from this song in my head.


View: https://youtu.be/9h7ZIJwGxJA

 

[JtB]

Wey hey that’s the shortest day out of the way