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Hello, I'm an astronomy student at the University of Virginia doing photometry on Saturn's moons in various wavelengths. I'm pretty new to IRAF, having only recently set it up on a virtual machine running Ubuntu Linux. My question is, are there any applications, techniques, or packages out there that would be good for removing the light gradient from Saturn's rings, in order to isolate the moons?Here's an example of the images I'm working with:

Hopefully you'll get other suggestions to this. There's nothing particular to dealing with Saturn in the system, my only thought is that you should look at some of the image mask making tasks (e.g. do a "cl> refer mask" command) to perhaps create a mask of the ring regions. You can then interpolate over these with background pixels or otherwise zero the values to get rid of them. This assumes however that the moons aren't overlapping the rings but are off in the sky somewhere. If not then what you need is some way to fit the light in the rings and the excess is the moon, but that would be custom code you'd need to write. If by 'isolate' the moon you mean simply for display purposes, then you can choose the display range to be used so the scaling is done for the approx intensity of the moon. Likewise, you can use an image section to isolate just the pixels around a particular object and eliminate everything else entirely. If you still have questions, post back.-Mike

Perhaps you could find the gradient yourself(manually), and then remove it from the image using the task IMEXPR. do "help imexpr" to see what it does but you can do complicated arithmetic on images with it.