Calendar solstice

[Cpt.Caveman]

When is the solstice?

[slothrop]

The 22nd.

[Dru]

? My calendar says Dec 21, 18:some odd hours Mtn Standard time.

 

I would guess 22 is Greenwich Mean Time, it will be tomorrow there by then.

Edited December 16, 2002 by Dru

[Cpt.Caveman]

Fair enough. Thanks

[slothrop]

Oops. Mine sez 12/22, 0115 UTC.

[Dru]

Yup UTC is Greenwich Mean Time I think. = Universal Time Control it sounds like something from Dr Who. I bet Greg W and Fairweather disapprove since it is universal not USA.

[slothrop]

Universal Time Coordinated, I think, which does imply a kind of international (gasp!) cooperation. I think Bush would probably be against it, if he knew it existed. Sssh!

[Cpt.Caveman]

We have to let the brits think they own something. Otherwise they'd never be our allies

[klenke]

According to this website: http://www.candlegrove.com/solstice.html#1999

 

"Winter solstice for 2002 will occur at 5:14 pm PST on December 21. If you want to be precise about it, please be sure to correct for your time zone."

 

And this site gives upcoming solstice dates and times:

http://aa.usno.navy.mil/data/docs/EarthSeasons.html

Note: Universal Time is the same thing as Greenwich Mean Time.

[COL._Von_Spanker]

Just curious, how does the solstice occur at an exact time? i'm no astonomer, so maybe I'm mixed up, but I thought the winter solstice was the just shortest day of the year. And where does the equinox fit into the picture?

[klenke]

A solstice is the exact time when a ray from the sun striking the earth's surface reaches its farthest point north or south of the equator. For our winter solstice, this is the time when this ray (making a perpendicular impact on the surface) reaches its farthest point south of the equator. This line of latitude is called the Tropic of Capricorn and is 23.5 degrees south of the equator. From the autumnal equinox until the winter solstice, the ray progresses southward from the equator to the ToC and from the winter solstice to the vernal equinox (spring equinox), the ray progresses back to the equator, eventually crossing it.

 

The reason the northern hemisphere day is the shortest at the winter solstice is due to 3-D geometry. Essentially, to be concise, at the winter solstice, the most possible bulk of the earth blocks the rays of the sun from hitting northern hemisphere points. The amount of blockage (thus amount of daylight) is dependant on the latitude of the point. For points above the Arctic Circle, the sun's rays are wholly blocked by the bulk of the earth for a duration of the time between equinoxes and is dependant upon the latitude above this circle. That is, there is no daylight at all for a duration of this half-year. At the north pole, there is no sunlight at all from the autumnal equinox all the way to the vernal equinox (roughly 182 days).

 

Comprende?

Edited December 17, 2002 by klenke

[mattp]

"At the north pole, there is no sunlight at all from the winter solstice all the way to the vernal equinox (roughly 91 days)."

 

And I don't like it when it gets dark at 4:30 p.m. Those poor bastard seals must really be depressed.

 

 

[ScottP]

We have to let the brits think they own something. Otherwise they'd never be our allies

I guess we feel obligated since they invented it (GMT, not the Solstice.)

The book "Longitude " is a pretty interesting story about it.

[Norman_Clyde]

I become completely obsessed with the solstice at this time of year. My wife tells me to turn on the Happy Light when she hears me babbling on, about how we'll only be losing ten more minutes between now and the Solstice, but how due to the Equation of Time, both sunrise and sunset are moving a few minutes later each day, so even though the days will soon be getting longer, until about New Year's I will have even less daylight for my early morning runs... I never felt a need to know this stuff until I moved to the Northwest. Now it's my strategy for waiting out the long dark winter.

 

I used to wonder how the solstice occurred at a specific second. The best way I have found to visualize this phenomenon is to picture the line of the ecliptic, which is the line the Sun follows against the (invisible in the daytime) stars through the year. It's a great big circle drawn at an angle, from north of the celestial equator to south. (The Celestial Equator is a projection of Earth's equator on the Celestial Sphere, which itself is an imaginary sphere in the sky that can be used to map celestial objects.) Anyway, at the equinoxes this line crosses the celestial equator, and at the solstices it's at the extreme north or south end of its boundary. If you imagine which invisible stars are behind the sun as it rolls by in the sky, you may be able to visualize what I mean.

 

Another way to observe this phenomenon is to take note of the position of the full moon at different seasons. The moon travels along the same path in the sky as the sun, give or take a few degrees. Because the full moon is on the opposite side of the sky from the sun, the full moon on any one night will follow the same path as the daytime sun 6 months earlier or later. The moon will be nearly full on the Solstice this year, and will be very high in the sky-- about as high as the sun will be on the summer solstice. It's one more coping mechanism of mine to note the position of the December full moon, and to remind myself that the sun will once again be that high come June.

[SEF]

At the north pole, there is no sunlight at all from the winter solstice all the way to the vernal equinox (roughly 91 days).

 

Hmm. Unless I am really mistaken, the winter "night" of the N pole should begin well before the winter solstice, correct? Isn't the solstice the middle of that "night"? Whatever the start or end, it is still a long night.

 

I think another explanation of winter solstice is when the earth's tilt relative to the sun with the S pole towards the sun and N pole away has maximized.

[klenke]

Yes, Steve F., you are correct. What I said is technically still true. However, the north pole's entire night lasts from the autumnal equinox to the vernal equinox.

 

That's what happens when you define things off the top of your head. I knew there was probably some error somewhere in my definition. Mistakes happen, are corrected, and are soon forgotten.

 

[Ade]

We have to let the brits think they own something. Otherwise they'd never be our allies

 

It was a consolation prize for conquering half the known world and building an empire on which the sun never set. The runners up, France captained by Napoleon, got the SI system. Some say they actually deserved to win but a run of poor away performances cost them the championship, culminating in a weakened team playing England at Waterloo after a drubbing in Moscow.

 

Originally billed as a friendly match at a farmhouse in the low country things rapidly got out of hand. A very contraversial eleventh hour substitution by Wellington of a Prussian back row in the second half cost the diminutive frenchman the match and relegation the Elba. Readers should note that although Anglo-French relations have always been strained but this was the icing on the cake as far as Paris was concerned.

[klenke]

" There is such a thing as too much beta "

 

Yeah, here's a case in point for your signature quote: what does your post have to do with this thread? We're talking about the solstice here, not England and France's historical dislike for each other.

[Off_White]

Read the whole thread Klenke, it connects back to Greenwich Mean Time via the notion we have to let the Brits win something. Classical brilliant thread morphing if you ask me.

[klenke]

...like I said.

 

But that's alright cuz the thread has run its course.

[RobBob]

klenke, isn't it true that the earliest sunset/latest sunrise do not coincide with the solstice? I think I lost a bet once on that.

[sk]

Do we have no Druids that post here to explain th timing and signifigance to us ???

[Dru]

but the shortest day and longest night do....

[klenke]

RobBob,

 

Here's what I know from memory: the day of the year for the Northern Hemisphere that has the least amount of sunlight is coincident with the December winter solstice. However, sunrise continues to move forward in the morning after the winter solstice for a number of days until some physical quantities match up. I don't remember what these quantities are. That may be what you lost the bet concerning.

 

So I did a little searching on the web, and this is what I found:

Take the quiz: http://www.jgiesen.de/Quiz/day/

Or read this technical stuff: http://www.sciencenet.org.uk/database/Physics/9812/p01298d.html

{It looks like I was on the right track with my memory, though not certain of myself.}

[Norman_Clyde]

The reason that the shortest day is not also the day of latest sunrise and earliest sunset is due to the Equation of Time. Basically, when the Earth is closest to the Sun in its orbit, it orbits faster, which means it has to rotate a little more than once around to be facing the sun again. The few extra minutes of rotation mean that both sunrise and sunset move later at this time of year. The earliest sunset is about Dec. 10, latest sunrise about Jan. 1st.