Kevin,
I'm assuming you are not in North America as another important
happening is that there is a Total Lunar Eclipse on this Winter
Solstice. The last time this happened was 1638. More detail can be
found at http://science.nasa.gov/science-news/science-at-nasa/2010/17dec_solsticeeclipse/
Also December 14th is not just for the numerically obsessed, if you
spend much time out side like I do cross country skiing, or some thing
else, you are very much aware of the time of sunset near the solstice.
Cheers,
John
On Dec 19, 2010, at 5:19 PM, Kevin Karney wrote:
Dear Colleagues
In the depths of a freezing Northern winter, there's time to think
about days of special interest. There are six significant solar
dates around this time of the year.
Three are special and probably known to all...
21st December - half an hour before midnight - the Winter Soltice
25th December - not only Christmas day, but one of the four days in
the year when the equation-of-time is zero.
3rd January - Perihelion when the Earth is closest to the Sun,
One day is perhaps of interest only to the serious heliochronometer
user...
23rd December - the day when the equation of time is changing at
its maximum rate of almost 30 secs/day
Two days are nothing more than obscure, except to the numerically
obsessed - or to those who like strange questions to ask on quiz
nights....
14th December - the day on which the Sun sets earliest in the day
29th December - the day on which the Sun rises latest in the day
See the graph below. If you wonder why this is so, it is because
there are two effects in play (a) the daily change in sunrise/sunset
as a result of declination change is minimal around the solstice and
(b) the effect of the equation of time with its large eccentricity
component as the Sun races forward towards perihelion.
p.s. the graphs are for 54 degrees North latitude; the y-axis scale
will change at other latitudes.
p.p.s. dates are UT - so they may vary with your local longitude.
Have a wonderful Christmas season.
Kevin Karney
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