Charles Messier was hunting comets. These 110 smudges kept fooling him, so he numbered them (1771–81). The hall is now a rite of passage for amateur astronomers. Magnitudes are visual; distances are modern consensus, not Messier’s.
Catalogue after Messier / Méchain as completed to M110. Types and popular names follow common planetarium usage. M102 is disputed (often NGC 5866). Distances are order-of-magnitude — galaxies in Virgo sit ~50–60 million ly; globulars in the halo a few tens of thousands.