sentences:  It was in searching in vain for the comet that Charles Messier found the Crab Nebula, which he at first thought to be Halley's comet.After some observation, noticing that the object that he was observing was not moving across the sky, Messier concluded that the object was not a comet.Messier then realised the usefulness of compiling a catalogue of celestial objects of a cloudy nature, but fixed in the sky, to avoid incorrectly cataloguing them as comets.