Messier 19, NGC 6273

Messier 19 is a globular cluster in the constellation Ophiuchus. It was discovered by Charles Messier in 1764; William Herschel was the first to resolve it into stars. It is the most oblate (elliptical) globular cluster known.

In small instruments, M 19 is visible as a small, 7th-magnitude glow, about 8° east of Antares; its ellipticity is easily seen. M 19 is rich and dense, with countless stars of magnitude 14 and fainter concentrated into a diameter of 17' across. In his more colorful language, Admiral Smyth saw M 19 as "a fine, insulated globular cluster of small and very compressed stars of creamy and white tinge and slightly lustrous to the center."

Two fainter globular clusters, NGC 6293 (mag 8.4, diameter 1.9') and NGC 6284 (mag 9.5, diameter 1.5') are located within two degrees of M 19.

Messier 19 is the most oblate globular cluster known, with an ellipticity of E3-E4. The deformation may have to do with its proximity to the Galactic Center. While about 28,000 light years away from our Solar System, it is only 5,200 light years from the galactic center. It is slightly more remote from us than the center of the Milky Way, located nine degrees above the galactic plane and slightly west of the Galactic Center.

Physically, M 19 is about 140 light years across, and has an absolute magnitude of about -9. It contains four known RR Lyrae variables, and is receding from us at 146 km/sec.