M-33 comparison image

This image partially illustrates how important additional "subs" (light exposures) are in helping to define an image. The M-33 on the left integrates the image on the right (15x3min exposures, collected on September 13) with an additional 60 minutes of subs (20x3min, collected on October 11, 2007).
The differences are subtle but nonetheless discernible. I note four:
First, the extent or sweep of the spiral arms has been clarified. The diffuse nature of M-33 leads to a very low surface brightness.
Second, there is more "texture" or overall detail to the image. The 45 minute exposure required smoothing via a Gaussian blur. The 105 minute combined stack has been smoothed, but only by a small amount.
Third, the hydrogen alpha regions (with the reddish tinge) stand out more clearly, not only in the named regions, but also as H-alpha is intermixed with the arms.
And finally, the overall coloration of the image is, to my eye, more pleasing, moving from a muddier-greenish tinge in the smaller stack to a "ruddier" and somewhat bluer coloration in the larger stack.

Acquisition and Processing
Acquisition and processing per usual. Stacks combined with IP. Composite image created with PS CS2.