NGC 6426, Globular Cluster
NGC 6426 is a globular cluster with an apparent brightness of 10.9mag and an extent of 4.2 arcminutes, located at a rather large distance of 67,000
light-years in the constellation of the Serpent Bearer (Oph). It was discovered in July 1786 by none other than F.W. Herschel with his 18.7" telescope.
The cluster belongs to concentration class IX, which is why it is only slightly condensed towards the center. Its mass is given as 117,000 solar masses
and its diameter as around 80 light-years. This makes it one of the smaller representatives of its kind. Its absolute magnitude is M= -5.4mag, which
corresponds to the luminosity of around 12,000 suns.
With a metallicity of -2.11, the stars of NGC 6426 are very metal-poor and contain just 0.7% of the heavier elements found in the Sun. The globular
cluster is therefore thought to be around 12.9 billion years old.
----------------------------------------------------------------------------------------------------------------------------------------------
In my 20" f/3 Dobsonian, the globular cluster appears at 270x as a faint sphere with a low surface brightness, with a slightly brighter center. The cluster
is partially resolved both at the edges and in the center and around 30 very faint individual stars can be seen. The background appears grainy. Some
brighter stars form star clumps near the center. The outer regions of NGC 6426 are quite wide.
Many brighter stars in the surroundings offer a nice contrast.
