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M109

NGC 3992

The penultimate object in the Messier Catalogue is a galaxy in the constellation of Ursa Major. In the sky, it falls less than a degree from the star Phecda or Gamma Ursae Majoris (also called Phad), distinctive as the southeastern star of the four that make up the 'share' or the Plough (or the 'bowl' of the Big Dipper).

M109 lies immensely far beyond the seven stars that make up the prominent shape of the Plough; those stars are comparatively close neighbours of the Solar System, while M109 is far beyond our own Galaxy at a distance of some 55 million light years. Some sources suggest even larger distances for this galaxy, but even the most conservative values make M109 the most distant of all the objects with Messier numbers).

This galaxy has a barred spiral form, with spiralling arms forming a disc of matter, but that disc is bisected by a broad bar running through the galaxy's core and out across its inner arms. M109 is one of the most important members of the Ursa Major Cluster of galaxies, spreading throughout the northern regions of the Great Bear, and that cluster is itself an outlier of the immense Virgo Supercluster. Within the Ursa Major Cluster, M109 is the brightest member of its own galactic group, a group to which it gives its name: the M109 Group.

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