NGC 6121, also known as M4, is a globular cluster located in the constellation Scorpius. It is approximately 7,200 light-years away from Earth and is one of the closest globular clusters to our planet. NGC 6121 contains hundreds of thousands of stars, with a notable population of red giants. Discovered by Jean Philippe Loys de Chéseaux in 1746, NGC 6121 is notable for its relatively low metallicity, which provides insights into the early universe. The cluster is about 75 light-years in diameter and is estimated to be around 13 billion years old, making it one of the oldest known star clusters.