IC 1311, Open Star Cluster
In the constellation of Swan one can find a large number of open star clusters. Among them are very well known ones like Messier 29 or Messier 39, but also
quite unknown clusters like IC 1311, which was discovered by Thomas Espin in 1893.
The distance to IC 1311 has large uncertainties - therefore the mean value from different sources was used. The result is therefore a distance of about 17,000
light-years. With the help of the apparent diameter of 3.5' the true cluster diameter can be determined to 17 lightyears. This is quite a decent value. Most of the
stars in IC 1311 are fainter than 14-15mag, so it needs a larger telescope to resolve the cluster.
It is embedded in a large gas cloud, but nothing can be seen visually. Interesting is the fact that about 15 arcminutes away a very faint planetary nebula named
"Patchick 6" can be found.
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At low magnification, in a 20" Dobsonian, you can see a medium bright diffuse light spot surrounded by many brighter field stars. One of them shines in a soft
yellow tone.
Only at magnifications of more than 200x it becomes clear that this is a very rich star cluster. The background glow is still clearly visible and appears grainy.
Within it flashes about 20-25 individual stars, all of the same brightness. Some are significantly brighter than the rest, but these are likely to be foreground stars.
The overall impression at 270x is really nice: glittering star dust embedded in the deep black of the universe. About 50 stars can be seen.
