NGC 6811 (Smoke Ring / Hole in a Cluster) -- Open Cluster in Cygnus
The Smoke Ring
NGC 6811 is a delightful, but under appreciated, open cluster in the Swan. It is often
referred to as the “Hole in the Cluster” or as the “Smoke Ring” and for good reason. In
smaller telescopes most of the cluster’s 250+ stars are below the resolution of the
telescope which jointly form a more-or-less solid smoky-blur with an obvious hole at its
center. On the night of the drawing, the smoke-ring was easy to see in my 6-inch refractor
from my suburban backyard.
However, the first time I viewed NGC 6811 was from a much darker location with a larger
18-inch Dobsonian-telescope and I struggled to see the smoke ring. The increase in the
number of stars that I could see with the 18-inch decreased both the smoky appearance
and the allusion of the hole in the cluster’s center. It is also the reason the smoke ring
can’t be photographed, as far as I know, because the increase in the dimmer stars
smothers the smoke ring.