Re: [Astrometrica] Re: Calculation of Residuals
Bob Elliott Apr 30, 2003
Hi Scott and list members.
I have been reading this discussion with a lot of interest and want to
emphasize the point that,"it's not the size of the residuals but their
consistency that is important".
I might suggest a graphical way of checking your Astrometrica reductions if
you have a copy of Bill Gray's Guide program. V 6,7 or 8 should work.
Guide and it's associated astrometric reduction program, Charon can be set
up to display a small symbol of your reduction solution on the star map.
The positions are stored in a file in Charon.dat in the Guide directory
called MPC.log. Edit the Charon.dat file to read the Astrometrica file
MPCOrb.txt and Guide will display the positions your Astrometrica
reductions on a star map with USNO 2.0 stars if you so choose. By right
clicking on the symbol Guide will take you to a dialog box where you can
select "More info". One of the items in the more info display is the date
and time of the observation. By clicking on that line Guide8 will bring
the asteroid to the location calculated by the current elements stored in
the Guide Mpcorb.dat file. By selectively clicking on each calculated
position you can move the asteroid along the asteroid's path and check for
the consistency of your reductions.
Herb Rabb has fine tuned Astrometrica to give excellent results and I would
trust the reductions and think that you should turn in what you have.
After all they are accurate to the nearest second if your clock is set.
That is much better that one minute for the ephemeris you might get. Most
of my errors have to do with hours not seconds. I still have my 3.5 inch
floppy with his DOS program on it that I started using in 1995.
Go for it.
Bob Elliott
750 Fall Creek
Incidentally I ran three images of the NEO 2003 HA through both
Astrometrica and Charon and the positions agreed to within 0.1 arc seconds.
However the magnitudes were about 0.3 magnitudes brighter in Astrometrica
than in Charon.