M 67

M67 is one of the oldest known open clusters, and by far the oldest of Messier's open clusters, being aged at 3.2 billion years in the Star Catalog 2000; Mallas/Kreimer quote an even higher, but probably outdated value of 10 billion years.

At this later stage of evolution, the open cluster M67 shows, in its Hertzsprung-Russell diagram, a well-developed red giant branch, while the main sequence ends to the hot blue end at spectral class A or F. It contains 11 bright K-type giants of absolute magnitude +0.5 to +1.5, and several stars scattered on the horizontal branch. However, it also contains some strange stars near the bluer main sequence, representatives of the so-called Blue Stragglers, the brightest of which is of spectral class B8 or B9 and mag 10, corresponding to a luminosity of 50 times that of the Sun.

According to Cecilia Payne-Gaposhkin, M67 contains nearly 200 white dwarfs.

Right ascension	08 : 48.3 (hours : minutes)
Declination	+12 : 00 (degrees : minutes)
Distance	2.25 (light-years*10^3)
Visual magnitude	6.1