Located 7,200 light-years from us, globular cluster Messier 4 is believed to be one of the closest globular clusters to Earth. It is also thought to be one of the oldest with an estimated age of 12.2 billion years.

Globular clusters are collections of hundreds of thousands of stars that are gravitationally bound together. M4 is estimated to be 50 to 75 light-years in diameter based on its size and distance.

M4 is located in the constellation of Scorpius, 1.3 degrees west of the brilliant red-giant star Antares. Shining at magnitude 5.4 and subtending an apparent size of more than 30 arcminutes (larger than the full Moon), M4 can be seen with the unaided eye under good conditions from a dark-sky observing site.

M4 is one of the smallest and most open globular clusters known. Because of its closeness to us, it would be spectacular if not obscured by thick clouds of interstellar matter in the region of Antares and Rho Ophiuchus.

It was discovered by Philippe Loys de Chéseaux in 1745-46 and listed in Charles Messier's catalog on May 8, 1764. M4 was the first globular cluster to be resolved, by Messier, into a cluster of stars.

M4 also contains an unusual central bar of stars, visible in this image running roughly vertically in the center of the cluster. The bar is 2.5 arcminutes long and consists of 11th magnitude stars. It was first noted by William Herschel in 1783.

North is to the top in the above image.

Messier 4 Catalogs: M4, NGC 6121 Object Type: Globular Cluster Magnitude: 5.4v Size: 36' Constellation: Scorpius Image Field Centered At: RA: 16h 23m 36s Dec: -26° 32' 20"