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How To Retrieve And Use Guide Star Catalog Coordinates

If your target is brighter than 15th magnitude, start by checking if the target is in the Guide Star Catalog (GSC).
If you find a target and are unsure that you have the correct target, extract a FITS file for the pointing and look at the rest of the field.
Note that nearby sources often have significant proper motion, which must be obtained from a source other than the GSC, e.g. the PPM or Hipparcos catalogs.
If your target is brighter than about 9th magnitude, coordinates derived from the Hipparcos Input Catalogue (HIC) will probably be listed instead (or as well).
These modified HIC coordinates will have a dummy plate ID of 56 and an epoch of 2000.
Plate 56 coordinates occasionally have errors as large as 6 arcsec and should not be used - uUse coordinates from the Hipparcos output catalog instead.

These instructions for using GSC will be superseded when GSC2 coordinates are certified for use in HST proposals.

EXAMPLE
Fill in the following information on the GSC page:

Coordinates: 19H 33M 27S +33H 12M 7S
J2000
Field Size: 1 arcmin

The GSC output will look like:

Guide Star Catalogue (copyright,AURA 1989,1992) 
Position (J2000) : 19 33 27.00 +33 12 7.0   Box (arcmin): 1.00 x 1.00 
No.Entries       : 3                        No.Selected : 3

Guide Star ID  H  M  S      D  M  S    err    Mag  err Bp Cl  Plt  n IIPDGBFN  Epoch 
    2659 1668 19 33 27.46 +33 12 35.5  1.2  14.70 0.48  1 30 000J  1 FFTFFFFF  1983.516
    2659  114 19 33 27.08 +33 12  7.1  0.1   6.59 0.00  4 03   56  2 TFTFFFTT  2000.000
    2659  114 19 33 27.52 +33 12  1.2  0.4   5.91 0.40  1 30 02TN  2 TFTTFFTF  1983.518
        (a)      (b)                   (c)      (d)           (e)                (f)

Key:
a) The first two numbers are the GSC ID # for the target.
b) The next six numbers are the J2000 coordinates.
c) The next number is the positional error in arcsec.
d) The next two numbers are the magnitude and error in magnitude.
e) Plt is the GSC Plate ID (or 56 for Hipparcos Input Catalogue).
f) Epoch is the date the guide star plate was taken (or 2000 for Hipparcos Input Catalogue).

If your target is 2659-1668, the information is formatted in RPS2 like:

   Target_Number: 
     Target_Name:        
 Alternate_Names: GSC2659-01668               
     Description:                  
        Position: RA = 19H 33M 27.46S +/- 0.1S,
                  DEC = 33D 12' 35.5" +/- 1.2",   
                  PLATE-ID = 000J 
         Equinox: J2000   
Coordinate_Source: GUIDE_STAR_CATALOG            
          RV_or_Z:                    
            RA_PM:                   
           Dec_PM:                   
            Epoch: 1983.516   <---- only include epoch if specifying proper motion 
  Annual_Parallax:                      
             Flux: V = 14.70 +/- 0.48   
         Comments: