Globular Cluster Messier 12
History
In May 1764 Charles Messier discovered another globular cluster, Messier 12, only 3.4° north of M 10, which appears somewhat larger but darker. As was the case with most globular clusters, Messier and Bode initially believed that these «nebulae» did not contain any single stars. About two decades later Sir William Herschel recognized the true nature of M 12 as a grouping of thousands upon thousands of single stars.
Physical Properties
The integrated spectral type of all stars in this globular cluster is F7. Published distances from M 12 vary from 16'000 to 24'000 light years. Presumably it is at the same distance as M 10. The true distance of these two clusters would then be about 2000 light years. M 12 approaches with a radial speed of only about 17 km/s. [4]
| Designation | NGC 6218 |
| Type | GCL (IX) |
| Right Ascension (J2000.0) | 16h 47m 14.5s |
| Declination (J2000.0) | -01° 56' 50" |
| Diameter | 16 arcmin |
| Visual magnitude | 6.1 mag |
| Metric Distance | 4.800 kpc |
| Dreyer Description | !! globular, vB, vL, iR, gmbM, rrr, st 10… |
| Identification, Remarks | M 12, GCL 46 |
Finder Chart
The globular cluster Messier 12 is located in the constellation Serpent Bearer (Ophiuchus) approximately where the imaginary connecting lines between the stars κ - ζ Ophiuchi and β - Yed Prior (δ Ophiuchi) cross.
Visual Observation
400 mm Aperture: The globular cluster M 12 is not easy to find, especially when the sky is so milky and bright that you can barely make out the stars of the Serpent Bearer, but once you find it in the 21 mm Ethos eyepiece, you are rewarded for your search with beautifully resolved stars all the way to the core region. With increasing magnification, more stars become visible in the core region. — 400 mm f/4.5 Taurus Dobsonian, Glaubenberg, 17. 6. 2023, Bernd Nies