M107
Messier 107 or M107, also known as NGC 6171, is a very loose globular cluster in the constellation Ophiuchus, and is the last globular cluster in the Messier Catalogue. It was discovered by Pierre Méchain in April 1782, then independently by William Herschel in 1793. Herschel described it as a "globular cluster of stars, large, very rich, very much compressed, round, well resolved, clearly consisting of stars". It was not until 1947 that Helen Sawyer Hogg added it and three other objects discovered by Méchain to the list of Messier objects. The cluster is located 2.5° south and slightly west of the star Zeta Ophiuchi.
M107 is close to the galactic plane at a distance of about 20,900 light-years from Earth and 9.8 kly (3.0 kpc) from the Galactic Center. The orbit of this cluster carries it through the galaxy between 9.2–12.4 kly (2.82–3.79 kpc) from the Galactic Center, with the perigalactic distance laying within the galactic bar region. It is an Oosterhoff type I cluster with a metallicity of –0.95[7] and is considered part of the halo population. There are 22 known RR Lyrae variable stars in this cluster and a probable SX Phoenicis variable.
