Expert: James Gort - 5/31/2005

Question
How can we measure magnitude of stars by a CCD camera? And how can we precisely do it?
Sincerely.


Answer
Hello Alireza,

Glad to see you're interested in pursuing some real science!  The short answer is easy, but the "correct" answer is much longer and I'll give you a few references to give you more details.

First, if you're interested in "Visual" magnitude, you'll need a good filter - one with a center wavelength of 5450 Angstroms and a bandwidth of 880 Angstroms.  You'll also need a list of "standard" stars for calibration.  Finally, you'll need some software - image processing software meant for astronomical purposes.  And that's it!  Basically, the software analyzes the distribution of pixels, and fits that distribution to the closest magnitude match.

Now for the details.  That's a bit too much for here, but the best two sources I know of are:  "Handbook of CCD Astronomy" by Howell and "A Practical Guide to CCD Astronomy" by Martinez and Klotz.  Not quite as good, but still covering the basics of photometry, is "The New CCD Astronomy" by Wodaski (available from http://www.newastro.com/newastro/default.asp) - that site also includes software.  Richard Berry also has some good CCD Imaging Processing Software (available from http://www.willbell.com).  

Hope that helps.  Good luck, and clear skies!

Prof. James Gort