[guide-user] Re: magnitude derivation in Charon

Bob Elliott Dec 31, 1969

At 10:34 AM 1/24/00 +0000, Lawrence wrote:
>I can now routinely get matches in Charon of asteroids but in all cases,
>its magnitude estimate is not credible. Looking closely, it correctly
>identifies the target and puts a large red cross-hair that covers the
>screen - as described in the Charon instructions. But! In the *red*
>summary, it quotes a mag figure that is nonsense, and then I realised
>that the figure is actually that derived under the **yellow** cursor
>(that can be anywhere at start-up) - not the red cross-hair. This is
>why all my magnitudes have all been wrong. When I move the yellow
>cursor on top of the cross, the magnitude then shows about right.
>
>Can someone clarify the correct sequence to obtain valid magnitudes
>during Charon's analysis?

Laurence: When using Charon you must always bring the yellow cursor over
the object you want to measure. as you move the yellow cursor around on the
image you will notice that the red line of data will change as you near an
object that is marked with a red dot.
the position written to the MPC.LOG file is the location of the
object marked by a red dot nearest the yellow cursor. What you are seeing
is the position and magnitude of the location near the yellow cursor and not
the position marked by the large red cross hairs on the image. BTW you will
only get residuals of measured objects if the yellow cursor is very close to
the calculated position of the object you wish to measure. The red cross is
the calculated position of the object using the elements stored in Guide (C)
the yellow cross position is the observed position as calculated by Charon
(O). The residuals are then (O-C) given in arc seconds in R.A. and Dec.
respectively. I made that mistake a few times when I started using Charon
and was dutifully reminded by Gareth that my positions were not acceptable.

So--- make sure that you move the yellow cursor to the image of the object
you want to measure on the ccd image before you click the "o" key to save it
to the MPC.LOG file.

Best regards,

Bob Elliott
750 Fall Creek