Messier 107, Globular Cluster
Messier 107 is a 7.8mag bright globular cluster in the constellation of the Serpent Bearer (Oph) and is around 22,000 light-years away from
Earth. It was first discovered in April 1782 by Pierre Méchain, but also independently nine years later by F.W. Herschel.
In long-exposure images, the cluster reaches a size of around 13 arcminutes, which corresponds to a true diameter of around 80 light-years. In
a telescope, however, only the innermost 30 light-years are clearly visible. The stars in Messier 107 are loosely scattered, which is why
the cluster belongs to concentration class X. The mass is given as 180,000 solar masses, while the absolute magnitude is stated as M= -7.1mag,
which corresponds to a luminosity of around 59,000 suns.
The age of the stars is thought to be just under 13.9 billion years. They would therefore belong to the oldest population of stars in the universe.
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In my 20" f/3 Dobsonian, Messier 107 appears quite small and compact even at a magnification of 270x. The central area is relatively large and
only weakly concentrated. A not very widespread halo stretches outwards. More than 50 individual stars with a brightness of less than 13mag can
be seen, but there are also some brighter stars.
Several bright stars in the vicinity provide a nice contrast.
