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Historically, when the Messiers list was being compiled in the late 1700's and the NGC/IC catalogues (late 1800s to early 1900s) our galaxy was largely considered to be the entire universe, so cataloguing was mainly concerned with objects considered to be within the Milky Way Galaxy.
It was not until the discovery of Cepheid variable's within M31 that the idea of other galaxies was accepted.
Malcolm
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