solstice geometry

[Norman Albers]

We all agree solstice, like December 22, is the point of maximal polar axis pointing away from the sun, and so it is the longest night and shortest day. Yet those of you who have been holding your breath for dawn to come earlier are dead. You are not illuded to see that mornings have come even later. I think I can see this as a sidereal shift at the sinusoidal minimum in which, for 2-3 weeks either side of the solstice, the pole angle hardly changes. Look at the numbers, given that the pole goes +/- 23 degrees or so in 13 weeks. The 'top of the roller coaster' is a bit broad. THE FACTS ARE THAT AFTERNOONS REACHED THEIR DARKEST ABOUT 2 WEEKS BEFORE SOLSTICE, AND MORNINGS ARE JUST AT THEIR DARKEST NOW. Look in your almanac.

[swansont]

IIRC it's an effect from the orbit that gives rise to the "equation of time" (represented by the analemma — that squashed figure-8 you see on a globe or map). We just had the perihelion, which does not match up with the solstice, and that skews the sunrise/sunset symmetry.

[Norman Albers]

Aha, a further variable! I would like to understand this before I die. <OK I have cogitated. Are you saying, Swansont, that since we arrive at perihelion we are at a maximum orbital speed and so get a bit behind our average sidereal change?>

[Norman Albers]

There's a lot to this and I will never trust a clock again. I will finish reading this cool ref: http://members.aol.com/jwholtz/analemma/analemma.htm

[swansont]

It's the earth as a clock that you shouldn't trust.

[Norman Albers]

I'm reading that the geographic poles wobble only a few meters every year. <EDIT> Doesn't this sound like earth rotation vis-a-vis the stars, or sidereal time, is fairly steady? <> Magnetic poles, on the other hand, are crazy. The North magnetic pole is moving toward Siberia at 50 kilometers per year. The South pole moves at 5 km/yr.