Messier 5 — Globular Cluster in Serpens

M5 is a spectacular globular cluster in the constellation Serpens (Serpens Caput), located about 24,500 light-years from Earth. It is one of the oldest known globular clusters at an estimated 13 billion years. The cluster contains at least 100,000 stars and has an apparent diameter of about 23 arcminutes — nearly the size of the full Moon. With a total luminosity equivalent to about 90,000 Suns, it is also one of the most luminous globulars in our galaxy.

Located about 23 arcminutes north-northwest of the star 5 Serpentis. At magnitude 5.7, M5 is visible to the naked eye under dark skies and is easy in binoculars as a bright round glow. A 4-inch telescope at 100x begins resolving the outer stars, while the core remains a brilliant unresolved blaze. An 8-inch or larger scope at 150-200x resolves stars well into the center, revealing a slightly elliptical shape. Often considered to rival M13 in beauty. Best observed from May through August.

Discovered by the German astronomer Gottfried Kirch in 1702 while observing a comet. Charles Messier cataloged it in 1764, describing it as a round nebula. William Herschel resolved it into stars in 1791, counting roughly 200 visible stars.