Messier 5 or M5 (also designated NGC 5904) is a globular cluster in the constellation Serpens.

William Herschel was the first to resolve individual stars in the cluster in 1791, counting roughly 200.

[11] RR Lyrae stars, sometimes referred to as "Cluster Variables", are somewhat similar to Cepheid type variables and as such can be used as a tool to measure distances in outer space since the relation between their luminosities and periods are well known.

The brightest and most easily observed variable in M5 varies from magnitude 10.6 to 12.1 in a period of just under 26.5 days.

[12] The cluster has been used to test for magnetic dipole moments in neutrinos, which could shed light on some hypothetical particles such as the axion.