This year the December solstice occurs 2006-12-22T00:22 UT, which around here is 16:22 PST on Thursday the 21st.
As I noted around the equinox last September, this solstice will be particularly special because according to the expressions officially sanctioned by the IAU there was no December solstice in 2003, 2004, and 2005.
At the 24th general assembly in the year 2000 the IAU adopted resolutions (old site
, new site
) which abandoned the equinox as the point of departure, or coordinate origin, for measuring celestial coordinates, and thus earth rotation. Because the new expressions did not use the equinox, they did not define any equinoxes nor solstices. The date of implementation for the new resolutions was 2003-01-01, and starting then there was no official way to calculate the moment of an equinox or solstice.
At the time of adoption in 2000 the IAU recognized that it would have to produce new expressions. At the general assembly in 2003 the IAU officially created groups to sponsor and approve the new expressions, but the work was already under way and the first paper containing them was published. By early 2006 all of the expressions had been reviewed and published. So in August the 26th general assembly of the IAU in Prague approved resolutions
in which number 1 officially re-created the ecliptic, equinoxes, and solstices.
So if you celebrate the solstice do so with extra vigor, for you never know when the IAU will next act to undefine the mathematics on which your party is based. Current Mood: geeky