BS: Solstice vs Earliest Sundown

Subject: BS: Solstice vs Earliest Sundown
From: Slag
Date: 13 Dec 06 - 10:32 PM

Due to the eliptical nature of Earth's orbit about the Sun, though we haven't reached Winter Solstice yet, we have already seen the earliest Sundown. At 40 degrees N. Lat. it was 1635 hrs. from about the 1st through the 14th (perihelion reached on or about the 10th, I believe, Earth's closest approach to the Sun). If you were to mount a camera on a fixed location and (with proper filters) snap a picture of the sun at the exact same time every day and then overlay the pictures you would see something that looks like a long strectched out "figure 8". They used to print this on globes and the technical name for it is "analema". I just now checked a little desk dictionary and the word is not in there. I know I have left out a few important details and interesting other points like the location of the tropics and precession of the axes, but hey Mudcatters! Have at it. Tell us what you know!

Subject: RE: BS: Solstice vs Earliest Sundown
From: Sooz
Date: 14 Dec 06 - 02:32 AM

I've just found this - http://www.analemma.com/
- clever stuff.

Subject: RE: BS: Solstice vs Earliest Sundown
From: Slag
Date: 14 Dec 06 - 03:05 AM

Very cool!

Subject: RE: BS: Solstice vs Earliest Sundown
From: Keith A of Hertford
Date: 14 Dec 06 - 05:14 AM

Perihelion is about 3rd/4th January, so a few weeks off yet.
It is the extra speed we have around this time that starts to make the sunset later while the days continue to shorten.
Sunrises get later.

Subject: RE: BS: Solstice vs Earliest Sundown
From: Keith A of Hertford
Date: 14 Dec 06 - 06:21 AM

Should have said that sunrises get even later (than sunsets so days still get shorter).

I will be asking questions later.

Subject: RE: BS: Solstice vs Earliest Sundown
From: katlaughing
Date: 14 Dec 06 - 06:23 AM

Very kewl!

Subject: RE: BS: Solstice vs Earliest Sundown
From: GUEST,Cats
Date: 14 Dec 06 - 08:56 AM

This solstice will be very special for us as we have worked out that our house is the only dwelling in the valley that lines up with the sunset on the winter solstice, having taken in and done the maths for the earths rotational movements. It also lines up directly with the Rillaton Barrow [where the gold cup was found - if you haven't seen it google it, it's worth looking at]. We know there have been people living on our site since 987, if not before, so this year we should be able to confirm the importance of the site.

Subject: RE: BS: Solstice vs Earliest Sundown
From: JennyO
Date: 14 Dec 06 - 10:28 AM

From the point of view of the Southern Hemisphere, where we are, the sunsets also continue to get later after our Summer Solstice in a few days, but whereas the days were getting longer before the Summer Solstice, the days start to get shorter after it - ie the sunrises start to catch up. Hope that makes some sort of sense!

Subject: RE: BS: Solstice vs Earliest Sundown
From: KateG
Date: 14 Dec 06 - 04:23 PM

Thanks for that tidbit! I'd already worked out that the sunrises kept getting later for about 10 days after the solstice, so it makes sense that the sunsets start getting earlier about the same amount of time before the solsice. My old globe (c. 1945) has an analemma on it, wasn't aware that they'd been discontinued.

Subject: RE: BS: Solstice vs Earliest Sundown
From: Slag
Date: 15 Dec 06 - 04:30 AM

Yeah, I had forgotten the spelling of it! It is such a handy device and lends so much to our understanding of the Earth's course and the effects it has on it's inhabitants.

Subject: RE: BS: Solstice vs Earliest Sundown
From: Desert Dancer
Date: 15 Dec 06 - 08:35 PM

I had a vague memory and went to look it up... wouldn't you know it:
www.analemma.com.

~ Becky in Tucson

Subject: RE: BS: Solstice vs Earliest Sundown
From: Desert Dancer
Date: 15 Dec 06 - 08:42 PM

Warning: there's a lot to wade through in that site I linked! For the info applicable to this discussion, click on "Other Phenomena".

~ B in T
whose old Windoze computer doesn't like Quicktime very much, unfortunately.

Subject: RE: BS: Solstice vs Earliest Sundown
From: EBarnacle
Date: 15 Dec 06 - 11:50 PM

Another piece of trivia with which to impress my friends--awri!

Subject: RE: BS: Solstice vs Earliest Sundown
From: open mike
Date: 16 Dec 06 - 02:01 PM

when my father worked in an office with a view of a large wall of a building out the window, he charted, or photographed the shadow of
his building where the corner of it was at noon each day for a year.
the graph of the points of the corner of the shadow looked like
that figure 8.....which is the symbol for eternity..

Subject: RE: BS: Solstice vs Earliest Sundown
From: skarpi
Date: 16 Dec 06 - 06:41 PM

its getting shorter day ........and darker ,every min
from Iceland
Skarpi

Subject: RE: BS: Solstice vs Earliest Sundown
From: Mrrzy
Date: 16 Dec 06 - 08:57 PM

All you need is the thied axis and you'll have the Lorenz butterfly!

Subject: RE: BS: Solstice vs Earliest Sundown
From: GUEST
Date: 17 Dec 06 - 02:35 PM

gullibility has been taken out of the dictionary

Subject: RE: BS: Solstice vs Earliest Sundown
From: JohnInKansas
Date: 18 Dec 06 - 10:10 AM

Pedant alert:

In the opening post:

Due to the eliptical nature of Earth's orbit about the Sun, ...

The ellipsicity to the orbit has at best an extremely minor bearing on the solstice/equinox occurances. These would occur even if the earth's orbit around the sun was a "perfect circle."

It's the inclination of the earth's axis of rotation relative to the perpendicular to the plane of the orbit that produces these effects.

The winter solstice, in the Northern Hemisphere, when things are "coldest" actually occurs very nearly at the point where the earth is closest to the sun, IIRC, so the "elliptic factor," if significant at all, should make things warmer, when the inclination is making them colder up north.

And later:

It is the extra speed we have around this time that starts to make the sunset later while the days continue to shorten

A somewhat dubious assertion requiring the "how do you define se ... "speed" question.

The observation that the earliest/latest sunrise is at a different time ("in" a different day) than the latest/earliest sunset, and neither is "in the same day as" the solstice/equinox is largely a matter of geometry. Easily observed but exceedingly difficult to "explain" with simple math, hence a visit to a planetarium with models is the best approach to at least an intuitive grasp of it all.

John

Subject: RE: BS: Solstice vs Earliest Sundown
From: Keith A of Hertford
Date: 18 Dec 06 - 10:20 AM

No John, the non solstice earliest/latest sunrise/sunset is indeed due to the higher /lower orbital speed at closest/furthest approach

Subject: RE: BS: Solstice vs Earliest Sundown
From: Liz the Squeak
Date: 18 Dec 06 - 11:06 AM

I don't care where the sun it, but right this minute outside my nearly west facing window, there is the most glorious pink and lilac sky.... it's stunning - just right for a Solstice week!

Blessed Be.

LTS