NGC 6910 - Rocking Horse Cluster

[DarkerSky]

The last couple of evenings (18-19 May) I've taken the opportunity to observe and sketch NGC 6910 in Cygnus. It is a small but obvious open cluster close to Gamma Cygni (Sadr). Used my 12" and got a widefield view with my 17mm Baader Hyperion so I could get Sadr and the cluster in the same FOV.

12" Orion Optics

x70 Magnification

TFOV 0.97 degrees

The cluster is known as the Rocking Horse Cluster. I couldnt fathom out why to begin with as I saw more of an inverted Y shape with the orientation of my view. When I rotated myself at the EP so that North was at the bottom of my view I could indeed make out the playful horse shape, with the brightest two yellow stars in the cluster forming the feet (or wheels!)

Im actually now wondering whether it should be a toy wooden horse - note the chain of stars that work northwards...reminds me a bit of a rope for pulling the horse along!

The two yellow stars in the cluster are intersting in their own right. The northernmost was the marginally brighter one of the pair, and was the brightest member of the cluster. It is spectral type K1 III.

The southernmost yellow star however is a variable stars - V2118 Cygni. It also has a spectral type B1, which you would assume would be white/blue. But it's not !! It's yellow!!

The reason for this I have read is that interstellar dust is dimming the visual appearance of the star, giving it the yellow appearance. Fascinating stuff - well I think so anyway