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In page Charles Messier:

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Messier's occupation as a comet hunter led him to continually come across fixed diffuse objects in the night sky which could be mistaken for comets. He compiled a list of them,[1] in collaboration with his friend and assistant Pierre Méchain (who may have found at least 20 of the objects[2]), to avoid wasting time sorting them out from the comets for which they were looking. The entries are now known to be 39 galaxies, 4 planetary nebulae, 7 other types of nebulae, 26 open star clusters and 29 globular star clusters.[citation needed]