M13

The Great Hercules Cluster is one of the brightest and best-known globular clusters in the northern sky, located about 22,200 light-years from Earth in the constellation Hercules. It contains roughly 300,000 stars packed into a sphere about 145 light-years in diameter. The cluster is estimated to be 11.65 billion years old, making it one of the oldest objects in the Milky Way. Its stars are metal-poor, typical of Population II stars formed in the early universe.

Located along the western edge of the Keystone asterism in Hercules, about one-third of the way from Eta to Zeta Herculis. Visible to the naked eye from very dark sites as a faint fuzzy star. Binoculars show a distinct round glow. A 4-inch telescope at 100x begins to resolve individual stars at the edges, while the core remains an intense, grainy glow. An 8-inch or larger telescope at 150-200x spectacularly resolves stars across the entire cluster, with chains and streams of stars radiating outward. Best observed from May through September.

Discovered by Edmond Halley in 1714, who noted it could be seen with the naked eye on clear nights. Charles Messier cataloged it in 1764. William Herschel was the first to resolve it into individual stars in 1783. In 1974, the Arecibo radio telescope beamed a message toward M13 — the famous Arecibo Message — as a demonstration of human technological achievement.