NGC 6939 (Lund 960, Cr 423) Open Cluster in Cepheus
Located at: RA 20 hours 31 minutes 32 seconds, Dec +60 degrees 39 minutes 14 seconds
Size: 7.0' (10') Magnitude: 7.8 Class: II 1 r
North is up
West to the right
8" f5 Newtonian reflector
ST-8XME, self-guided, binned 1x1, temp -15c, camera control MaxIm DL 4.56
Lumicon Red filter, 340 minutes (34 x 10 minute subs), 07/15/16/2008; seeing 2.9-3.2 FWHM per CCDStack
CCDStack 1.3.7, Photoshop CS5.1
Rolling Roof Observatory, Thousand Oaks, CA 91360 (+34d 13m 29s -118h 52m 20s)
This rich open cluster is located just under 40 minutes NNW of the large spiral galaxy NGC 6946 (NGC 6946 @8F5 / @14.5F5). The dim little sliver of a galaxy to the southwest (lower right) is UGC 11583 (2.3'x0.6', mag 14.3, Cl: Irr).
According to "Star Clusters", by Brent Archinal and Steven Hynes, the size of this open cluster is 10 arc minutes.
From the NGC / IC Project:
Contemporary Visual Observation(s) for NGC 6939
NGC 6939 = Cr 423 = Mel 231 = Lund 960 20 31 30 +60 39.7 V = 7.8; Size 8 18" (10/9/04): beautifully rich cluster of ~150 star in a 10'-12' triangular region over haze. Beyond the ends of the triangular vertices are four 10th magnitude stars with the star towards the ENE an easy double. The cluster is fairly uniform with a rich clump of a half-dozen stars near the center. A number of the stars are in chains, including a string of equally spaced 12-13th magnitude stars along the south side which is oriented NW-SE. N6946 (which was sporting a supernova) lies 40' SE and both can be placed in the same low power field. 18" (8/17/04): this triangular-shaped rich cluster is beautifully framed in the 160x field (24'). The cluster is enclosed within a kite asterism of four mag 10 stars with two of these stars near the east and west vertices of the triangular outline. ~125 stars are visible in a 10' diameter, with most of the stars mag 12-14. Just west of center is a very rich 3' group and just following this group is a small knot of 4 very faint stars. The west side is well-defined by a string of mag 12 stars oriented NW-SE. 17.5" (9/14/85): about 100-140 stars mag 12-15 are resolved. Difficult to count as stars fill the 22' field at 220x with no distinct boundaries. N6946 is located less than 40' SE. 13" (7/27/84): ~80 stars resolved but richness makes an accurate count difficult. 13" (7/5/83): ~70 stars resolved at 166x, very rich, beautiful in faint stars. - by Steve Gottlieb