M4

M4 is the nearest globular cluster to our solar system, at only about 7,200 light-years away in Scorpius. Despite being relatively loose and diffuse for a globular, it contains tens of thousands of stars spread across about 75 light-years. A distinctive central bar of 11th-magnitude stars runs through the core, making it unique among globulars.

Located just 1.3 degrees west of Antares (Alpha Scorpii), making it very easy to find. Visible to the naked eye from dark sites. Binoculars show a large, diffuse glow. Even a small telescope resolves individual stars — M4 is one of the easiest globulars to resolve due to its proximity and loose concentration. Look for the characteristic bar of stars across the center at 100x. Best observed from May through August.

Discovered by Philippe Loys de Cheseaux in 1745-46. Charles Messier cataloged it in 1764. It was possibly the first globular cluster in which individual stars were resolved. In 1987, the first millisecond pulsar in a globular cluster was discovered in M4.