Object Name: Messier 3
Alternative Designations: NGC 5272
Object Type: Class VI Globular Cluster
Constellation: Canes Venatici
Right Ascension: 13 : 42.2 (h:m)
Declination: +28 : 23 (deg:m)
Distance: 33.9 (kly)
Visual Brightness: 6.2 (mag)
Apparent Dimension: 18.0 (arc min)
Locating Messier 3: For binoculars, the easiest way to discover this ancient beauty is to look about halfway between the pair of Arcturus and Cor Caroli, just east of Beta Comae. Many times, just starting at Arcturus and sweeping slowly up towards Cor Caroli is enough! If you still have trouble, locate the Coma Berenices star cluster (Melotte 111) and look east about a fist width. You’ll find it 6 degrees north-northeast of Beta Comae and it will show very easily in the finderscope. In binoculars of all sizes and even under urban lighting conditions, Messier 3 is very bright and will begin to show some signs of resolution with larger models, such as 10X50. Even small telescopes will see individual stars come to life and it will explode into a fine, pinpoint mass in telescopes as small as 6″.
What You Are Looking At: This ball of approximately a half-million gravitationally bound stars is one of the oldest formations in our galaxy. At around 40,000 light years away, the awesome M3 globular cluster spans about 220 light-years and is believed to be as much as 10 billion years old. To get a grasp on this concept, our own Sun is less than half that age! M3 is 40,000 years away, traveling at the speed of light; yet we can still see this great globular cluster with the slightest optical aid. Further away than our own galactic center, Messier 3 commands 760 light years of area – keeping the stars within that distance tied to its rich core. It contains at least 170 RR Lyrae variables – along with a surprising number of Blue Straggler Stars – blue main-sequence stars which appear youthful. Since all stars in globular clusters are believed to be about the same age, it is possible these stars have had their outer layers stripped away while passing through the dense core region of M3.
History: Oddly enough, this huge ball of stars was only the 76th deep sky object ever seen by human eyes and equipment when it was discovered by Charles Messier on May 3, 1764. Although Charles had logged his previous two discoveries, it was the third that prompted him to begin his now famous catalog of ‘objects that are not comets’. Said Messier in his notes: “On May 3, 1764, when working on a catalog of the nebulae, I have discovered one between Bootes and one of the Hunting Dogs [Canes Venatici] of Hevelius, the southernmore of the two, exactly between the tail and the paws of this Dog, according to the charts of Flamsteed. I have observed that nebula on the meridian, and I compared with Mu Bootis; its right ascension has been found as 202d 51′ 19″, and its declination as 29d 32′ 57″ north. That nebula which I have examined with a Gregorian telescope of 30 pouces focal length, which magnifies 104 times, doesn’t contain any star; the center is brilliant, and the light gets lost fading [outward]; it is round, and could have 3 minutes of arc in diameter. One can see it in a good sky with an ordinary [nonachromatic] refractor of one foot [FL] , it doesn’t contain any star, its center is brilliant, and its light is gradually fading away, it is round; in a beautiful [dark] sky.”
Of course, Sir William Herschel was the first to resolve it into stars: “To these may added the 1st, 3d [M3], 27, 33, 57, 79, 81, 82, 101 [of Messier's catalog], which in my 7, 10, and 20-feet reflectors shewed a mottled kind of nebulosity, which I shall call resolvable; so that I expect my present telescope will, perhaps, render the stars visible of which I suppose them to be composed…” But none described it more eloquently than Admiral Smyth: “A brilliant and beautiful globular congregation of not less than 1000 small stars, between the southern Hound and the knee of Bootes; it blazes splendidly towards the centre, and has outliers in all directions, except the sf [south following; SE], where it is so compressed that, with its stragglers, it has something of the figure of the luminous oceanic creature called Medusa pellucens. This noble object is situated in a triangle formed by three small stars in the np [north preceding; NW], nf [north following; NE], and sf [south following, SE] quadrabts, which, by their comparative brightness, add to the beauty of the field. It is nearly in mid-distance between the Arcturus star and Cor Caroli, at 11deg north-west of the former star. This mass is one of those balls of compact and wedged stars, whose laws of aggregation it is so impossible to assign; but the rotundity of figure gives full indication of some general attractive bond of union. It was discovered in 1764 by Messier, who described it as “a nebula without a star, brilliant and round:” his instrument must have been rather moderate not to resolve this object, and it is matter of regret, that the exertions of such a man were straitened to such means. It was next pronounced to be a “mottled nebulosity;” but in 1784, Sir W. Herschel attacked it with his 20-foot reflector, and resolved it into a “beautiful cluster of stars, about 5′ or 6′ in diameter.” By the gauging process, which he has fully described, he estimated its profundity to be of the 243rd order.”
May your observations be as rich!
B&W image thanks to Palomar Observatory, courtesy of Caltech and color image thanks to N.A.Sharp, Vanessa Harvey/REU program/NOAO/AURA/NSF.