We continue our marathon of objects from the catalog of Charles Messier with another globular cluster, M3, also known as NGC 5272. This cluster is located in the constellation of Canes Venatici and is one of the most visible clusters of the sky, along with M5 and M13 . The M3 globular cluster is about 33,900 light years from Earth and has an estimated age of 10 billion years.
The M3 globular cluster is far from easily recognizable stars. The alignment of the beta and gamma stars of the constellation Coma Berenices can certainly help, or the star Arcturus can be useful for locating it at least approximately. Its declination is such that it can be seen, at different times of the year, in both hemispheres. The best time to observe it in Europe is spring. Its apparent magnitude is equal to +6.3, which makes it barely observable to the naked eye in exceptional visual conditions. The cluster is already visible with binoculars like a faint speckle, but with a 20 cm telescope it reveals all its majesty, although it is naturally appreciable even with smaller diameters.
The star cluster was discovered by Charles Messier in 1764 and it was his first real original discovery. Later it was the subject of intense observational campaigns by William Herschel. Thus wrote Messier about this cluster:
Nebula discovered between Bootes and one of Hevelius’s Hunting Dogs; it does not contain any stars, its center is brilliant and its light diminishes insensibly, it is round; with a beautiful sky it can be seen with a telescope from one foot; it is reported on the comet chart observed in 1779. Memories of the Academy of the same year. Observed March 29, 1781, always beautiful.
Like all globular clusters, M3 is also made up of very ancient stars, about 500,000, with a peculiarity: inside, in fact, a young blue star of spectral class O8 was found. The latter would be a blue straggler, a very particular class of stars whose origins are still now a mystery to astronomers. According to the most accredited theories, be dealing with stars formed by the fusion of other stars, or the collapse of a binary system. Furthermore, the globular cluster M3 contains 274 variable stars, many of them of the RR Lyrae type, the highest number ever observed in globular clusters.