#122: Messier 39

I first made the acquaintance of this wide open star cluster in late July of 1971.  I was observing with my Tasco Lunagrosso 4.5” Reflector.  It was also the summer of a very favourable opposition of Mars.  Life was good!  I wrote at the time: “A very large open cluster of stars, mostly white.  The object filled about half of my field of view at 22x, and all of my 45x eyepiece.  At the lower power I counted about 25 stars, several of them 6th and 7th magnitude, although some were much fainter.  M 39 is a very pleasant cluster to view, and easy to locate.”

Cut to late August, 1978.  I am now using my Edmund 8” Reflector, the big red beast!  My notes from then:  "M 39 is a cluster so bright and widely scattered that it is seen very well in the 9 x 30 finderscope [virtually a 1” scope].  This also makes it a very worthwhile object for binoculars.  36x and 56x suited this very loose group.  I stopped the scope down to 4”, and the group was splendid to view!  Indeed, full aperture added nothing but more brightness, and a few much fainter stars.  At full aperture, an interesting way to view this cluster is to put it well out of focus.  My favourite view was at 56x and 4” of aperture, however.  A lovely wide pair of stars lies near the very center (ARN 78: 7.6-8.8/52”).”  Two other doubles with bright primary stars are just south.

In late September of 2013 I observed it with my Orion 12” Dob.  “The cluster looks best at low power.  It is suitable for a 2” refractor and anything larger.  I used 43x and 60x, where the cluster appears like a slightly more condensed version of the Pleiades.  The stars are nearly blinding in a 12” mirror.  Not a rich cluster, but very bright and well scattered.”  And I did indeed view it in Space Eye more recently, my wonderful 2” refractor, declaring it a minor showpiece for that instrument.

 https://skyview.gsfc.nasa.gov/current/cgi/runquery.pl?Interface=bform&VCOORD=ngc+7092&SURVEY=Digitized+Sky+Survey&SCOORD=Equatorial&EQUINX=2000&MAPROJ=Gnomonic&SFACTR=0.35&ISCALN=Linear&GRIDDD=No&COLTAB=B-W+Linear&PIXELX=600&PIXELY=600

I consider M 39 a great summer object to show people who are new to telescopes.  It makes an immediate impact, and rewards longer views with the bright double stars, as well as the many fainter members.  For experienced observers an interesting side trip can be made to oc Platis 1, marked as Anon Platis on Unronometria Chart 32.  Lying ½ degree north and 2' preceding (west) the Messier object, this tiny cluster will reward viewers with scopes of 8" or higher.  The region around Messier 39 is littered with small clusters and interesting star fields, and makes a good starting point for some low power meandering.

M 39 (oc 7092):  Size 31’; Mag. 4.6; Br. star mag. 7.

Oc Platis 1:  Size 10’; Br. star mag. 8.9.

Clear skies.

Mapman Mike