A normal sundial has the gnomon coaxial with the Earth. This is
done to keep the errors with respect to clock time to a minimum during
the course of the year. If we have the ambition to make our sundial
read clock time to better than +/- 15 minutes, then we have to correct
for the Equation of
Hi moondialists:
I have been watching the waxing moon each night as it heads towards the
total lunar eclipse on January 21 4:41:30 Universal Time. Its apparent
diameter seems to be increasing, which means that it is approaching perigee,
right? If last month's huge full moon was nearly at
Earlier I wrote:
According to the 2000 Astronomical Almanac, perigee occurs Jan 19 23 h
UT. According to Kepler an orbital body moves fastest near perigee
(equal area rule). The faster motion may outweigh the larger umbra--I
don't know, though I suspect this to be the case.
On the web page
Hi moondialists:
I have been watching the waxing moon each night as it heads towards the
total lunar eclipse on January 21 4:41:30 Universal Time. Its apparent
diameter seems to be increasing, which means that it is approaching perigee,
right? If last month's huge full moon was nearly at
The synodic month (full moon to full moon) averages 29.53 days, while
the anomalistic month (perigee to perigee) is 27.55 days, so the phases
drift with respect to perigee.
see: http://www.treasure-troves.com/astro/AnomalisticMonth.html
