[BAA Comets] CCD Astrometry and Photometry procedure

[Roger Dymock]

Good afternoon all,

I have made a minor change to the procedure showing how the Astrometrica Centroid facility can be
used to position the cross hairs centrally over the head of the comet. 

Previously I had expressed concern that the procedure may not produce accurate magnitudes for comets
brighter than mag 10. Recent measurements by Kevin Hills and myself show this not to be the case and
we have both obtained good results to mag 8. 

Examining images that had given inaccurate measurements I noted that;
- one was over exposed
- one was under exposed (due to fast moving comet) and part of the image was cut off by the dome or
shutter

Do please let me know if you experience problems measuring the magnitudes of bright comets using the
subject procedure.

Regards

Roger Dymock
Email: roger.dymock at ntlworld.com
Tel: 023 92647986
Skype: rogerdymock67 or
Skype: rjvdymock
MPC Observatory Code: 940
Project Alcock http://www.britastro.org/projectalcock/