Bill's update of Guide on 6 Jan has a very neat feature that allows one to
plot astrometric positions on Guide. It reads the data file that one
generates in Charon and plots the position on the Guide display. I used
this last night to plot several positions of comet LINEAR (C/1999 Y1) after
being disturbed by the large residuals that charon was giving me. The
positions when plotted all fell along a line parallel to the ephemeris that
Guide had generated and plotted for my finding chart. I could then right
click on the mouse and draw a line through my observations to see what kind
of scatter I had. The positions looked quite good but just displaced below
and to the east of the ephemeris trail of the comet. I then turned on the
line of variation feature in guide and set it for 0.1 day. My "line of
positions" crossed the line of variation about 0.083 days behind the comet.
It looked to me that the comet was about two hours behind schedule. I
e-mailed Syuichi Nakano in Japan and asked him if he had an updated orbit
for the comet which he very kindly sent me. With the new set of elements
loaded into Guide my observations all fall right on the ephemeris for comet
1999 Y1. Since Charon consistently gives me astrometric positions better
than 1 arc sec from the predicted position and I was getting residuals of
almost 30 arc sec it was nice to be able to check that I wasn't doing
something stupid which is often the case. I have set the default file to
MPC.LOG which is where Charon puts the astrometric positions and they get
automatically plotted on the finding chart as the night progresses. The
instant feedback is a good check on how the observations are going when the
brain is getting foggy.

As always, much thanks to Bill Gray.


Bob Elliott
750 Fall Creek