Messier 80 (also known as NGC 6093) is a globular cluster in Scorpius. It was discovered by Charles Messier in January of 1781. William Herschel was the first to resolve it into stars; he described it as "one of the richest and most compressed clusters of small stars I remember to have seen."
Messier 80 appears about 4° NW of Antares, midway between α Sco (Antares) and β Sco (Graffias) in a rich Milky Way field filled with bright and dark nebulae. At visual magnitude 7.3, M 80's appearance resembles that of a faint comet, without a tail. M 80 is a compact globular cluster, and can be easily seen in small telescopes as a mottled ball of light. Visually, M 80 shows a well-resolved 10' diameter disk. The more prominent stars fall along curved strings on the globular's northern and western edges.
Four times farther away than M 4, at an estimated distance of 32,600 light-years, M 80's spatial diameter is about 95 light-years. It contains several hundred thousand stars, and is among the more densely populated globular clusters in the Milky Way Galaxy. M 80 contains a relatively large number of "blue stragglers", stars that appear to be much younger than the cluster itself. It is thought these stars have lost part of their outer layers due to close encounters with other cluster members, or perhaps as the result of collisions between stars in the dense cluster. Images from the Hubble Space Telescope have shown districts of very high blue straggler densities, suggesting that the center of the cluster is likely to have a very high capture and collision rate.
In May of 1860 a nova was discovered in M 80 that attained a magnitude of +7.0. This nova, with the variable star designation T Scorpii, reached an absolute magnitude of -8.5, briefly outshining the entire cluster, and is one of the two known novae to have occurred in a globular cluster.