[Aavso-photometry] (no subject)

[Dirk Terrell]

On Thu, 18 Aug 2005 09:19:00 -0600, Keith Graham wrote:

>It is well known that s/n can be improved by stacking images. I was wondering if stacking the same image onto itself would serve the same purpose as stacking several images taken separately. I tried this by saving the same image using different names so I could load them all into my image-processing program and stack them. I did find that my s/n and uncertainty improved immensely. 

Uh, no. That's the photometric equivalent of a perpetual motion
machine. :-) Stacking is similar to averaging measurements and you're
averaging the same measurement over and over, so you'll get the same
answer. You appear to be getting better S/N because the gain you're
using is no longer valid.

Dirk

---
Dr. Dirk Terrell
Computer and Mission Systems Section Manager/Astronomer
Southwest Research Institute, Boulder, CO
303-546-9670
http://www.boulder.swri.edu/~terrell/