The two images of M2 shown below were both taken thru Kopernik's 20-inch Optical Guidance Systems F/8.1 Ritchey Chretien Cassegrain. The first is a recent color image taken with an SBIG STL 1301E CCD camera, while the second is an older black & white image taken with an SBIG ST-9E camera processed to show the full extent of the cluster.
Maraldi (Sept. 1st, 1746): "This one is round, well terminated and brighter in the center, about 4 or 5 arc minutes in extent and not a single star around it to a pretty large distance; none can be seen in the whole field of the telescope. This appears very singular to me, for most of the stars one calls nebulous are surrounded by many stars, making one think that the whiteness found there is the effect of the light of a mass of stars too small to be seen in the largest telescopes. I took, at first, this nebula for the comet."
Charles Messier(Sept. 11th, 1760): "Nebula without star, center brilliant; surrounded by a circular light resembling the nucleus of a comet. (Diameter 4 arc minutes)."
PROFESSOR VINCE: who saw M2 in William Herschel's 40 foot telescope in Sept. 1779, wrote afterwards, 'The scattered stars were brought to a good, well-determined focus, from which it appears that the central condensed light is owing to a multitude of stars that appeared at various distances behind and near one another. I could actually see and distinguish the stars even in the central mass.'
SMYTH: ‘A fine globular cluster. This magnificent ball of stars condenses to the center and presents so fine a spherical form that imagination cannot but picture the inconceivable brilliance of their visible heavens to its animated myriads.'
Globular Cluster M-2 in the constellation of Aquarius is about 50,000 light years away, and 150 light years in diameter. (But Click here for the latest news on Globular Star Cluster distances and ages!!) Maraldi discovered the cluster in 1746, and Charles Messier rediscovered it in 1760. One of the richer and more compact globular clusters, it gains in impressiveness through its position in a rather blank portion of the sky. The cluster has at least 100,000 stars, the brightest of which are red and yellow giants with absolute magnitudes of about 3. As a comparison, consider that our Sun at such a distance would appear as a star of magnitude 20.7, just detectable with a 10 minute CCD exposure using Kopernik’s 20 inch telescope. M-2 is about half a million times more luminous than the Sun.
M-2 is one of the finest Globular Star Clusters in the sky. It is easily seen in small telescopes and even binoculars, but it takes at least an 8 inch telescope to resolve it.
George Normandin, KAS
July 7th, 2007