Messier catalogs the Whirlpool Galaxy (M51)
DOI: 10.1063/PT.5.031070
On this day in 1773 Charles Messier was continuing his search for fuzzy objects in the night sky, which, being fixed, might confuse comet hunters. When he pointed his 10-cm refracting telescope at the constellation Canes Venatici (the Hunting Dogs), he discovered the 51st of his fuzzy objects, which now goes by the names M51a, NGC 5194 and the Whirlpool Galaxy. Later observations with better telescopes revealed M51a to be a spectacular face-on spiral galaxy interacting with a dwarf galaxy companion. The two images below, both from the Hubble Space Telescope, show optical emission (left) and near infrared (right). Both images show starlight. The principal difference between the two is that the near IR is less easily blocked by dust than the optical.
Date in History: 13 October 1773
