IC 4996, Open Star Cluster
IC 4996 is a small open star cluster in the middle of the constellation Swan, discovered in 1896 by Hugo Clemens.
It is located about 3° south of "Sadr" and therefore quite easy to find. Recent measurements from 2019 put the cluster at a distance of 6,200 light-years.
Since it is located in the middle of the Milky Way and behind the so-called "Great Rift", the stars of IC 4996 are weakened by 1.8 magnitudes due to the
dust located there. The age is given with 8 to 10 million years - so the cluster is quite young.
The brightest star belongs to spectral class B0 and therefore has a surface temperature of nearly 30,000 Kelvin. With an absolute brightness of -6.0mag
it shines 26,000 times brighter than our sun. A blue super giant.
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In a 20" telescope at low magnification of 120x a small and bright concentration of stars is immediately noticeable. Since the cluster is relatively small
and concentrated, you can easily increase the magnification to 200x and more, at which many fainter stars can be seen. Most noticeable are three bright
stars, which dominate the cluster and also form the center. The other members of the cluster are much fainter and come out best at 270x. Then about 30-35
individual stars with very different brightnesses can be seen.
