A globular cluster is a tightly packed group of stars that orbits a galaxy. These clusters can contain thousands to millions of stars, all held together by their mutual gravity. They are typically found in the halo of a galaxy and are much older than most stars in the galaxy, often containing stars that are billions of years old. Globular clusters are spherical in shape and can be observed with telescopes. They are important for studying the formation and evolution of galaxies, including our own Milky Way. Some well-known globular clusters include M13 in the constellation Hercules and Omega Centauri.