OT: Solstice

[Bill Ricker]

> It's actually the other way 'round. The earth is closer to the sun on
> the winter solstice.

Closer, but not quite closest!

Solstice and Equinox are defined in terms of sun angles (declination)
and length of daylight, and has to do with tilt of the axis of Earth
wrto to Sun. On Solstice, the axis of spin is in the same plane as the
earth-sun plane perpendicular to the orbit, and at (local) noon, the
sun is directly overhead at one Tropic or the other, named for the
star-sign in which it happens (T of Capricorn and Cancer). Equinox has
the axis perpendicular to the sun-earth plane, and the sun is overhead
at the Equator at local noon.

Since the actual alignment is instantaneous, there is a TIME of
solstice and equinox.
2006
Perihelion  Jan   4 15    Equinoxes  Mar   20 18 26    Sept  23 04 03
Aphelion    July  3 23    Solstices  June  21 12 26    Dec   22 00 22
http://aa.usno.navy.mil/data/docs/EarthSeasons.html

Nearest/farthest are Perihelion/Apohelion, also know Perisol/aposol,
when the earth crosses the major axis on its orbit and thus has a
minimum or maximum distance to the near focus of the ellipse, Sol. In
general, these are called periapsis and apoapsis; of an earth orbit,
perigee and apogee.
http://mathworld.wolfram.com/Periapsis.html
http://scienceworld.wolfram.com/physics/Orbit.html

The dates of solstice (and equinox) oscillate, thanks to year%day
remainder (leap years).
http://scienceworld.wolfram.com/astronomy/WinterSolstice.html

Wikipedia have "friendlier" diagrams.
http://en.wikipedia.org/wiki/Image:Earth-lighting-winter-solstice_EN.png
http://en.wikipedia.org/wiki/Image:North_season.jpg
http://en.wikipedia.org/wiki/Solstice

-- 
Bill
n1vux at arrl.net bill.n1vux at gmail.com