The stars in globular clusters orbit about a common center of gravity, so these clusters are usually spherical. Some globular clusters, like Messier 19, have a slightly elongated shape. This cluster is only 6,500 light-years away from the center of our Milky Way galaxy, so the gravity and tidal forces from the massive galactic center could be causing M19 to stretch out.
|Visible From Pacific Northwest||Mid April to August|
|Best Time To Observe||July|
|Minimum Size Of Viewing Device||Binoculars|
|Object Type||Globular Cluster|
|Designations||Messier 19, M19, NGC 6273, GCl 52, C 1659-262, MWSC 2519|
|Right Ascension||17h 02m 37.69s|
|Object Radius||70 light years|
|Distance From Earth||28,700 light years|
Charles Messier discovered the cluster on June 5, 1764 and he described it as a “nebula without stars, on the parallel of Antares between Scorpius and the right foot of Ophiuchus: this nebula is round; one can see it very well with an ordinary telescope of 3.5-foot [FL]; the nearest neighboring known star to this nebula is 28 Ophiuchi, which is of mag. 6, according to Flamsteed. (diam. 3′)”
William Herschel was the first to dissolve the cluster into individual stars. In 1783, he observed M19 in a 10-foot telescope and noted, “With 250, I can see 5 or 6 stars,a nd all the rest appears mottled like other objects of its kind, when not sufficiently magnified or illuminated.” In 1784, Herschel identified the object as a cluster after observing it in a 20-foot telescope. He described M19 as a “cluster of very compressed stars, much accumulated in the middle; 4 or 5 minutes diameter.”
Locating M19 In The Sky
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 appears as a fuzzy patch of light in 2-inch binoculars. Amateur telescopes will show a cluster about 6 arc minutes in size visually and 13.5 arc minutes photographically. The cluster’s elliptical shape is evident even in small instruments. A 10-inch telescope, on the other hand, will reveal the cluster’s bright core about 3 by 4 arc minutes in apparent size and a halo occupying a region 5 by 7 arc minutes in size.
As with any cluster of stars, precise auto guiding will be crucial as making sure the stars are crisp is crucial to any image. There aren’t a plethora of guides available for those looking to specifically imaging M19, as the best one could potentially find would be on astobin or astropixels. It is definitely possible with a modified DSLR, but will require a telescope with guiding to track M19.
Sources And Further Reading
Descriptions of all of Messier Objects can be found here.