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Re: Asteroid astrometry




  John wrote:

> What about this data on 773 Patrick has found?
> 
 ...
> But the positions measured for 773 are a bit different to the orbit
> predictions, far more so than the case with most TASS objects and GSC
> stars for example.

  I just checked this.  I took the positions for this object
from the TASS frames, as quoted in Patrick's E-mail.  I used the
JPL Horizons Ephemeris system

          http://ssd.jpl.nasa.gov/cgi-bin/eph

to calculate the position of asteroid 773 as observed from Tom's
location in Batavia, IL, on the night in question (2002 Feb 14, 
between 6:00 and 7:00 UT).   The JPL ephemeris gave me positions
which differ from those quoted by Patrick several arcseconds
(and the JPL ones turn out to be closer to the measured positions
than Patrick's ones).

  I compared the measured and predicted positions at two
times, around 6:21 UT and 6:46 UT.  "Delta" means
(measured - predicted).

                            delta RA           delta Dec
           6:21 UT        +2.9 arcsec        +1.4 arcsec
           6:47 UT        +0.9 arcsec        -1.4 arcsec

  I haven't (yet) done a careful analysis of the Mark IV astrometry,
but I'm quite willing to believe that these values lie within
the uncertainty of the Mark IV measurements (especially if it
turns out that the asteroid was observed near the edge of the frames).

> Does Tom need to get his lat and long and an MPC station number? 
  ...
> Does someone with experience need to take these bits of data and put
> them into the right format for forwarding to the MPC?
  ...
> I can guess Arne is going to say too soon for that sort of thing yet,

  I'll beat Arne to it and say, "Yes, it's too soon for that yet."
I (or someone else) needs to do a careful analysis of the accuracy
and precision of Mark IV positions.  But I (or someone else) needs
to do this _soon_; you are certainly right about that.

                                           Michael Richmond