The smallest open cluster

[Darren Drake]

NGC 1931 is I believe the smallest open cluster to be found in backyard scopes. It has some associated nebulosity and definitely worth finding. I saw it last night and saw 4 stars in the nebulosity in my light polluted back yard. I'm wondering how many individual stars can be seen through other scopes in darker skies...

[Don Pensack]

It looks like maybe a dozen or a few more stars right on the edge of a nebula that sort of resembles a galaxy.
This is an interesting object pairing and is best at fairly high power for me (in a 12.5").
Here is an photographic image that comes very close to the visual image I see in dark skies:
http://www.google.com/imgres?q=ngc1931&um=1&hl=en&client=opera&sa=N&rls=en&tbm=isch&tbnid=3lX15HNN4fK4DM:&imgrefurl=http://cs-observatory.com/Q8%2520Nebulas.htm&docid=qFpPCYx7mejzwM&imgurl=http://cs-observatory.com/Q8%252520Images/Nebulas/NGC1931-020410.jpg&w=1820&h=1350&ei=lqBCT-m0BarZiALA_eG-AQ&zoom=1&iact=hc&vpx=187&vpy=248&dur=1802&hovh=193&hovw=261&tx=141&ty=124&sig=113718308628045922436&page=2&tbnh=149&tbnw=199&start=21&ndsp=25&ved=0CNUBEK0DMCE&biw=1579&bih=694

[Sue French]

Listed open cluster sizes vary from source to source, sometimes a lot, but Archinal and Hynes' Star Clusters gives NGC 1931 a size of 6.0'. There are quite a few smaller clusters according to the book, but among those I know to be visible in backyard scopes, you might like to try NGC 6846, listed at 0.8'.

Sue

[Marko]

I too felt that visually the central dense tiny area must have been the cluster and noted it as very tiny. This is often the case when an obscure cluster is in a blanket of stars I'll note the ones that 'seem' to be the cluster. There are apparently many other stars around it that are also in the cluster. The earlier observation was discussing other stars in the field, perhaps in this cluster. More recently when observing open clusters I'll tend to indicate if the full cluster was obvious or if a surrounding blanket of stars made the limits of the cluster questionable.

A re-observation of mine in an 18" (for Herschel I list) sites the tiny group as the cluster: (which is only a little bit of this one)
3-27-09: 40" dia. Sort of 1.5EL 70dPA nebulosity. Tight EQ tri star formation in center about 15" on edge

An earlier observation in an 11" SCT is a bit more vague but does discuss other stars that perhaps are part of it afterall.
2-19-06 Hcoe 11”f6.3: Difficult. On 1 side of long rectangle of star pattern