NGC 6755 & NGC 6756 -- Open Clusters in Aquila
Two Clusters in the Eagle
The Open Clusters NGC 6755 and NGC 6756 are about ½ degree apart, making them
both visible together in the low power eyepiece for most telescopes. However, they are
very different. The larger and brighter NGC 6755 sticks out far easier in light polluted
skies than the dimmer stars of the smaller cluster NGC 6756. Under darker skies with a
larger telescope both are easily seen, and I would argue that NGC 6756 concentrated
glow makes it even easier to recognize as an Open Cluster than the spread-out
NGC 6755. From a suburban site, the trick in finding the uniform glow of NGC 6756,
which is made up of around 13 magnitude stars, is to up the magnification a bit if you are
having difficulties locating it. Having said that, on a good clear night, like the one I made
this drawing, I really did not have problems finding NGC 6756 with the six-inch telescope
from my suburban home.
Many electronic and hardcopy star atlases list the Open Cluster Czernik-39 within the
boundaries of NGC 6755. Its approximate location in my drawing would be just to the left of
the “N” in the NGC 6755 label. Other star atlases do not mention it. I cannot make it out (in
any size telescope) and personally doubt that it exists – or at the very best it is just a
concentrated part of NGC 6755. The literature is as confusing as the star atlases are. I am
going to go with Archinal & Hynes excellent 2003 book “Star Clusters” that Czernik-39 is a
synonym (in-part) of NGC 6755 – at least until I hear or see additional information.
both visible together in the low power eyepiece for most telescopes. However, they are
very different. The larger and brighter NGC 6755 sticks out far easier in light polluted
skies than the dimmer stars of the smaller cluster NGC 6756. Under darker skies with a
larger telescope both are easily seen, and I would argue that NGC 6756 concentrated
glow makes it even easier to recognize as an Open Cluster than the spread-out
NGC 6755. From a suburban site, the trick in finding the uniform glow of NGC 6756,
which is made up of around 13 magnitude stars, is to up the magnification a bit if you are
having difficulties locating it. Having said that, on a good clear night, like the one I made
this drawing, I really did not have problems finding NGC 6756 with the six-inch telescope
from my suburban home.
Many electronic and hardcopy star atlases list the Open Cluster Czernik-39 within the
boundaries of NGC 6755. Its approximate location in my drawing would be just to the left of
the “N” in the NGC 6755 label. Other star atlases do not mention it. I cannot make it out (in
any size telescope) and personally doubt that it exists – or at the very best it is just a
concentrated part of NGC 6755. The literature is as confusing as the star atlases are. I am
going to go with Archinal & Hynes excellent 2003 book “Star Clusters” that Czernik-39 is a
synonym (in-part) of NGC 6755 – at least until I hear or see additional information.