M4 - CAT'S EYE GLOBULAR

Messier 4 is the closest globular cluster to our solar system, lying only about 7,200 light-years away in the constellation Scorpius, just 1.3 degrees west of the brilliant red supergiant star Antares. This proximity makes it one of the easiest globular clusters to observe and resolve into individual stars, even with modest amateur telescopes. M4 contains an estimated 100,000 stars spread across a diameter of roughly 75 light-years. It was first discovered by Philippe Loys de Cheseaux in 1746 and later cataloged by Messier in 1764. One of M4's most distinctive features is a prominent bar-shaped structure of 11th-magnitude stars running through its center, sometimes called the "bar of M4," which is visible in telescopes of 4 inches or larger. This feature makes M4 easy to identify and distinguishes it from other globular clusters. M4 has been an important target for professional astronomers and the Hubble Space Telescope, which has used it to study white dwarf cooling sequences and has identified some of the oldest known white dwarfs in the Milky Way, estimated to be about 13 billion years old. The cluster also contains a millisecond pulsar and at least one confirmed exoplanet orbiting a pulsar-white dwarf binary system, making it a scientifically rich object. Its relatively loose concentration (Class IX) means that individual stars can be resolved across the entire face of the cluster with moderate-aperture telescopes.

Spans approximately 75 light-years across with about 100,000 stars, located only 7,200 light-years away, the nearest globular cluster to Earth.