[Aavso-photometry] FITS test results so far

[Michael Koppelman]

It is certainly enlightening to see how these different software 
packages handle this. Clearly in most cases if images are combined the 
TIME-OBS keyword needs to be managed manually.

I almost never combine images and then do photometry. I always do 
photometry and then average the photometry if I find I need to beat the 
errors down. This allows me to do a weighted average if the 
uncertainties are not equal. It also takes out the extra math involved 
with registering and rotating images if there is some slight change in 
the field over time. It's hard for me to think of a reason why one 
would stack images before doing photometry. Can anyone help me?

Cheers,
Michael Koppelman
http://www.lolife.com/astronomy/