I was looking at some data,

http://aa.usno.navy.mil/data/docs/EarthSeasons.html

I could not figure out why the duration between Winter solstice and the
immediately
following perhelion jumps around. We know that the perhelion should
advance one
day on our calendars about every 71 years. So you would think there
should be about
a 2o minute increase from one year to the next. Anybody have an
explanation?

Tom