APOD: 2024 September 26 - The Great Globular Cluster in Hercules

Good morning, Rallypoint, and welcome to the September 26th edition of Astronomy Picture of the Day (APOD). Charles Messier cataloged it in 1764 (and dubbed it M13), but Edmund Halley first noted this 'little patch' in 1716. A globular cluster is a concentrated grouping of stars bound together by gravity, with a greater density of stars towards its center: in M13, stars are about 500 times more concentrated than in our solar neighborhood (Alpha Centauri is an estimated 4 light years from our Sun).

Some believe there are over 1,000,000 stars collected into the Great Globular Cluster in Hercules. Lying 25,000 light years from Earth, scientists estimate its age to be at least 14 billion years old. M13 was selected in 1974 as target for one of the first radio messages addressed to possible extra-terrestrial intelligent races, and sent by the (now offline) big radio telescope of the Arecibo Observatory.