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With DSO it is difficult to know which objects will be visible just by looking at their magnitude. While a magnitude 9 star will be easily visible because the light is a single point, a magnitude 9 DSO such as a galaxy will have that light spread over a larger area. Imagine taking that same star and defocusing it until the light is spread over the same area in the eyepiece as the galaxy, I'm sure you can understand what I am saying.
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