M2 is a rich compact globular cluster at the edge of naked eye visibility that's located in the constellation of Aquarius. It's an easy binocular object (mag. +6.3) but requires a dark site with extremely good seeing conditions to be spotted with the naked eye.
M2 was discovered on September 11, 1746 by French astronomer Jean-Dominique Maraldi while observing a comet with Jacques Cassini, the son of legendary Italian astronomer Giovanni Cassini. Charles Messier then rediscovered it exactly 14 years later. He described the cluster, like many of his other objects, as "a nebula without any stars associated with it". William Herschel was the first to resolve individual stars in 1783.
Finding M2 can be initially challenging as it's located in a relatively sparsely populated area of sky. The key is to locate the two brightest stars in Aquarius, Sadalsuud (β Aqr - mag. +2.90) and Sadalmelik (α Aqr - mag. +2.95). Sadalsuud is positioned 10 degrees southwest of Sadalmelik and located 5 degrees north of Sadalsuud is M2. Together the two stars and the globular cluster form a large right-angled triangle.
M2 straddles the celestial equator and is therefore visible from all over the World, although it appears higher in the sky when viewed from tropical latitudes. It's best seen between July and October.
Through 7x50 or 10x50 binoculars, M2 appears obviously non-stellar like an out of focus star. A small 80mm (3.1-inch) telescope at high powers reveals a bright centre surrounded by a small fuzzy halo in an otherwise barren field of view. Close by is a pair of 6th/7th magnitude white stars that point almost directly towards the globular.
A medium size 200mm (8-inch) telescope will resolve some of the outer stars of which the brightest are of mag. +13.1. Higher magnifications certainly help, although the globular doesn't quite have the wow factor of M13 and other great southern clusters, it's still an impressive sight. Larger scopes of the order of 300mm (12-inch) or greater reveal many stars scattered across the complete face. It also appears elliptical in shape with a peculiar dark lane that crosses the north-east edge.
As Messier globulars go, M2 is relatively distant at 37,500 light-years. However, it's intrinsically large and therefore despite the distance covers a respectable 16 arc minutes of apparent sky. The cluster is estimated to be 13,000 million years old and contains about 150,000 stars.
M2 Data Table
|Object Type||Globular cluster|
|RA (J2000)||21h 33m 29s|
|DEC (J2000)||-00d 49m 23s|
|Apparent Size (arc mins)||16 x 16|
|Age (years)||13 Billion|
|Number of Stars||150,000|