Archive for September 2013

NGC 6791 – Pencil Sketch And Image – Open Cluster In Lyra Which Can Be Very Difficult! The Complete Observers Challenge Link Is Posted At The Bottom Of This Entry.

September 21, 2013
  • Date:  August 26,  2013
  • Time:  11:00 PM EDT
  •  Location:  Foothills of North Carolina
  •  Naked Eye Limited Magnitude:  5.0 
  • Temperature:  60’s  Humidity:  90%
  •  Seeing:  Fair  Transparency:  Fair
  •  Telescope:  10-inch f/4.5 Newtonian 
  • Magnification:  44x  Field of View:  1.3 degrees

 NGC 6791 is a faint and difficult open cluster from my moderately light polluted backyard.  I first became interested in this cluster over twenty years ago, after reading 1000+ The Amateur Astronomer’s Field Guide To Deep-Sky Observing by Tomm Lorenzin.  I had also read other observing reports describing this cluster, so I could hardly wait to see this cluster “glorious sprinkle of over three hundred stars” as described by others.  

On that night in 1993, I attempted to locate the cluster, but couldn’t see anything.  I checked my atlas again, to make sure my scope was pointed at the correct location.  I increased the magnification from 57x to 114x, but still no luck.  Conditions were only fair on that night, and the late summer haze in North Carolina can make faint objects even more difficult.  I changed the magnification again, going back to 57x, and then I spotted a very faint haze.  A little field motion seemed to help.  I could see some brighter stars superimposed over the cluster, but no resolve of the primary stars of the cluster.

Almost twenty years to the day, on the night of August 26th 2013, I was able to get a better look at this cluster.  Using my 10-inch reflector with a magnification of 44x, I was again able to see a faint haze in the background. My description of open cluster, NGC 6791 is as following:

The cluster appeared as a very faint glow with a somewhat elongated shape, oriented N-S.  I could count about eight fairly bright foreground stars, but in the darkness behind these stars was a sprinkling of maybe 35 very faint stars.  Averted vision was required, and the faint stars of the cluster seemed to sparkle.  What a beautiful sight!  The fainter stars seemed to be far in the distance behind what I perceived as foreground stars.  The most noticeable feature is a chain of three brighter stars on the SW edge of the cluster.  The middle star in the chain has a fainter companion, which makes a total of four stars, but this additional star required at least 100x to see.  I can now easily locate this cluster by looking for this small star chain.  

The following sketch was made using a blank 5 x 8 note card, and a No. 2 pencil.  The colors were inverted using my scanner.

Roger Ivester

NGC 6791 - OC - Lyra

The following image is by Dr. James Dire from Hawaii


Complete Observers Challenge Report: AUGUST 2013 OBSERVERS CHALLENGE – NGC-6791