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Are there two ways of determining surface brightness?
By way of example, take M33/NGC 598 - the pinwheel galaxy in Triangulum.
Cartes Du Ciel has the magnitude at 5.7, whereas Astroplanner has it at 6.2. Okay, not a huge discrepancy, I guess. But the former puts the surface brightness at 14.2, whereas Astroplanner puts it at 23.5! In fact all of Astroplanners objects seem to have very low surface brightnesses in the 20's.
Astroplanner's 23.5 is kind of *almost 4 times the 6.2 visual magnitude, but not quite.
I thought the equations for surface brightness were pretty established and derived from the object's magnitude and size. CDC's mag 14.2 makes sense in that the difficulty of seeing the object is roughly about as hard as a 14.2 magnitude star, but the Astroplanner version at 23.5? I don't even know what that figure means?
Is there a way to convert this number so I can see if it falls below the limiting magnitude of my scope?
Markus
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