NGC 6366, Globular Cluster
NGC 6366 is a very faint globular cluster in the constellation of the Serpent Bearer, which was first discovered by August Winnecke only in 1860
because of its low brightness.
With an apparent brightness of around 9.5mag and an extent of 13', it belongs to concentration class XI. From the known distance of around
11,000 light-years, the absolute magnitude can be calculated as M= -5.5mag, which corresponds to a luminosity of just 16,000 suns. The mass
of the globular cluster is given as 38,000 solar masses, the diameter is only 50 light-years, with the core radius measuring only 6.4 light-years.
The metal-rich stars are still gravitationally bound to the cluster up to a distance of 110 light-years.
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In my 20" Dobsonian, NGC 6366 was visible next to a bright asterism as a large patch of light with low surface brightness, which could be
partially resolved into individual stars at 210x.
The view was even better at 270x. The globular cluster was completely resolved from the peripheral areas right into the core and over 50 faint
individual stars were visible, as well as some brighter ones scattered loosely over the entire cluster. The center appears only slightly brighter,
so the cluster looked very weakly concentrated.
