Messier 19

M19 is a globular cluster located in the southern constellation Ophiuchus at right ascension 17h 02m 37.69s, declination -26°16’04.6”. The cluster has an apparent magnitude of 7.47 and lies at a distance of 28,700 light-years from Earth. It has the designation NGC 6273 in the New General Catalogue, and also known as GCl 52, C 1659-262, MWSC 2519. Messier 19 is one of the most oblate known globulars. It has a distinctly elongated shape in the north-south direction. The oblate appearance may not accurately reflect the cluster’s physical shape because of the intervening dust and gas along the eastern edge of M19. The flattening is far less noticeable in infrared images. It is a class VIII globular cluster, which means that it is loosely concentrated toward the centre. The cluster is quite rich and dense, and it occupies an area 17 arc minutes in apparent diameter, corresponding to a linear diameter of 140 light-years. The cluster lies close to the galactic centre, at a distance of only about 6,500 light-years, which puts it on the other side of the Milky Way centre from our solar system. (The Sun is about 25,000 to 28,000 light-years distant from the rotational centre of the galaxy and M19 is 28,700 light-years away from the Sun.) The tidal forces of the galactic centre could explain why M19’s shape deviates from that of a globular cluster. The cluster has a mass about 1.1 million times that of the Sun and its estimated age is about 11.9 billion years. It is receding from us at 146 km/s.

Charles Messier discovered the cluster on June 5, 1764, and included it in his list of comet-like objects. William Herschel was the first to dissolve the cluster into individual stars.

Messier 19 is located 4.5 degrees to the west-southwest of Theta Ophiuchi, a relatively bright multiple star systems in the southern part of Ophiuchus constellation, marking the celestial serpent bearer’s right foot. Theta Ophiuchi has the spectral classification B2 IV and an apparent magnitude of 3.26. The cluster lies about 8 degrees east of Antares, the brightest star in Scorpius constellation, or roughly a fourth of the way from Antares to Kaus Borealis, the bright star that marks the tip of the Teapot asterism in Sagittarius. There are two other globular clusters in the vicinity of M19: NGC 6293 lies 1.5 degrees to the east-southeast of M19 and has an apparent magnitude of 8.4, and NGC 6284 has a visual magnitude of 9.5 and can be found 1.6 degrees to the north-northeast of M19.

Messier 19 contains a number of variable stars, including four Cepheids and RV Tauri type stars, and at least one RR Lyrae type variable with a known pulsation period.  The cluster has four confirmed RR Lyrae variables. The brightest stars in the cluster are 14th magnitude and the average visual magnitude of the 25 brightest stars is 14.8. Credits: Messier Objects, NASA, Universe Today, Wikipedia.