M3 is a fine globular cluster located in the northern constellation of Canes Venatici. It's widely considered by amateur astronomers to be one of the best examples of its type in the northern section of sky beaten only really by M13. With an apparent magnitude of +6.2, M3 is beyond naked eye visibility except from extremely dark sites. However, it's easily visible with binoculars appearing distinctly non-stellar. The cluster is best seen from northern latitudes during the months of March, April and May.
M3 lies in the southern part of Canes Venatici practically on the border with Boötes. It's located 12 degrees northwest of first magnitude orange giant star Arcturus and about halfway along an imaginary line connecting Arcturus with Cor Caroli (α CVn - mag. +2.9). The area of sky surrounding M3 is rather barren, but when observed through binoculars a number of 6th and 7th magnitude stars are visible along with the cluster itself. One such 6th magnitude star is just 0.5 degrees southwest of M3.
Popular 7x50 and 10x50 binoculars show M3 as a hazy spot not unlike an out of focus star. When viewed under good conditions, an 80mm (3.1 inch) scope or 20x80 binoculars reveals a large diffuse ball with a hint of graininess. Medium size instruments of the order of 150mm (6-inch) or 200mm (8-inch) aperture, display a large and bright diffuse ball of mottled light with a noticeably brighter core. Under dark skies, a number of stars are resolvable towards the outer edge with averted vision revealing many more. Through larger telescopes of the order of 300mm (12-inch) or greater, M3 is a spectacular sight covering much if not all of the field of view. The component stars are scattered in every direction and under black skies it's resolvable to the core. The apparent size is 18 arc minutes.
M3 was discovered by Charles Messier on May 3, 1764 and was first resolved into stars by William Herschel around 1784. It's located about 33,900 light-years from Earth and is a large globular cluster, estimated to contain at least 500,000 stars. With an age of about 8 billion years, M3 is young. It also contains a large number of variable stars. At least 274 exist, more than any other globular, of which 133 have been determined to be of the RR Lyrae type.
M3 Data Table
|Object Type||Globular cluster|
|RA (J2000)||13h 42m 11s|
|DEC (J2000)||+28d 22m 32s|
|Apparent Size (arc mins)||18 x 18|
|Age (years)||8 Billion|
|Number of Stars||>500,000|
|Notable Features||A much studied globular cluster. It contains at least 274 variables stars.|