M33 (NGC598), the Pinwheel Galaxy, is the biggest in relative dimensions (after M31) visible over the entire sky. It's a member of the Local Group, a galaxies cluster including also our own Milky Way. The surface brightness of this object is very low, and is difficult to observe it also under very dark skies. Into M33 can be seen several red emission nebulae, each one labeled with an NGC number.

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