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

Telescope:

 8" f5 Newtonian reflector

Camera:

 ST-8XME, self-guided, binned 1x1, temp -15c, camera control MaxIm DL 4.56

Image:

Lumicon Red filter, 340 minutes (34 x 10 minute subs), 07/15/16/2008; seeing 2.9-3.2 FWHM per CCDStack

Processing:

CCDStack 1.3.7, Photoshop CS5.1

Location:

 Rolling Roof Observatory, Thousand Oaks, CA 91360 (+34d 13m 29s -118h 52m 20s)

Notes:

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