Messier 12
Messier 12 or M12 (also known as NGC 6218 ) is a 6.1 like bright globular clusters with a diameter of 16 ' in the constellation Ophiuchus ( Ophiuchus ). Of the 5 globular clusters of the constellation (M9, 10, 12, 14 and 107 ), he is therefore the lightest.
He was discovered on May 30, 1764 by the French astronomer Charles Messier - one day after his "twin", the 3 ° southeast lying M10. But in 1783 it was William Herschel resolved into individual stars. His son John recognized his richness, A. Smyth a bright ring of stars around the center and Lord Rosse in 1850 indicated a spiral structure.
With about 250,000 solar masses M12 belongs to the larger globular clusters and the inner galactic halo, from which he never more than 20,000 light -years away in 130 million years orbital period.
In a 10 -x -50 - binoculars you can see a small, blurred discs, similar to the adjacent and spatially near globular cluster Messier 10 However, in a telescope with 10-15 cm aperture affects its center scattered about the same age as the M10, and in the six- to eight- inch easily recognizable bright individual stars from 12 size are structured loose.
The wide center measures 2 ½ ', some star chains extend to 10' diameter, the recently up to the limiting magnitude of 20 mag is even estimated at 30 '. Among the five variables are two RR Lyrae and Cepheid dwarfs.
It is assumed that the globular clusters has lost about a million stars at one or more passages through the Milky Way due to tidal forces, which is about four -fifths of its original mass.
Literature and links
- Ronald Stoyan: Atlas of the Messier Objects - The Highlights of the Deep Sky, p.92 - 93rd Oculum -Verlag, Erlangen 2006
- Bernd Koch, Stefan Korth: The Messier Objects - The 110 classic goals for sky watchers. S.32/33, Kosmos Verlag, Stuttgart, 2010
- Commons: Messier 12 - album with pictures, videos and audio files
- Mass loss of M12