Universe Today
Description:
“In the solar neighborhood and in most stellar clusters, the least massive stars are the most common, and by far. Our observations with ESO’s VLT show this is not the case for Messier 12... It is however clear that Messier 12 is surprisingly devoid of low-mass stars. For each solar-like star, we would expect roughly four times as many stars with half that mass. Our VLT observations only show an equal number of stars of different masses.”
"Our results indicate that NGC 6218 is very homogeneous as far as heavy elements are concerned. On the other hand, light elements involved in the well known proton-capture reactions of H-burning at high temperature, such as O and Na, show large variations, anticorrelated with each other, at all luminosities along the red giant branch. The conclusion is that the Na-O anticorrelation must be established in early times at the cluster formation."
History of Observation:
"In the same night of [May] 30 to 31, 1764, I have discovered a nebula in Serpens, between the arm and left side of Ophiuchus, according to the charts of Flamsteed: That nebula doesn't contain any star; it is round, its diameter can be 3 minutes of arc, its light is faint; on sees it very well with an ordinary [non-achromatic] refractor of 3 feet [FL]. I have determined its position, by comparing with the star Delta Ophiuchi; its right ascension has been concluded at 248d 42' 10", and its declination at 1d 30' 28" south. I have marked it in the chart of the apparent path of the Comet which I have observed last year [the comet of 1769]."
"...has stragglers in lines and branches extending some distance from the most condensed part, which is 3' diam. Comes almost up to a blaze in the middle, has a * 10.11 m in the centre. Very rich globular cluster. The stars are of 10th to 16th magnitude; very gradually much brighter toward the middle, but has stragglers in lines and branches extending some distance from the most condensed part, which is 3' in diameter. Comes almost up to a blaze in the middle, has a star of 10th or 11th magnitude in the centre."