Deep Sky
M35

NGC2158

M35 – Open Cluster
NGC 2158 Open Cluster
Constellation Gemini

The bright blue stars are part of M35, top of the image, anywhere between 100 to 10,000.  They have in common is the fact that they were formed at about the same time.  M35 is some 2800 light-years from earth, and relatively young at 150 million years old.  They are spread out over a 30 light-year distant.  NGC 2158 is some four times more distant and ,as the yellow indicates, over 10 times older(800 million years old) and much more compact.  Still considered a open cluster (I disagree should be considered a globular cluster), and intermediate-age.
Carol Christian has quite an article about 2158

10 images
20 second
23 Mar 12