Messier 4 or M4, aka NGC 6121 is a globular cluster in the constellation of Scorpius.
It was discovered by Philippe Loys de Chéseaux in 1745 and catalogued by Charles Messier in 1764.
M4 is conspicuous in even in Binoculars or the smallest of telescopes as a fuzzy ball of light, but with the average amateur telescope it resolves into a rather loose sprinkling of golden stars.
It appears about the same size as the Moon in the sky. It is one of the easiest globular clusters to find, being located only 1.3 degrees west of the bright star Antares, with both objects being visible in a wide-field telescope. Modestly sized telescopes will begin to resolve individual stars, of which the brightest in M4 are of apparent magnitude 10.8.
M4 Globular Cluster measures 75 light-years across. It features a characteristic “bar” structure across its core, visible in moderate sized telescopes. The structure consists of 11th-magnitude stars and is approximately 2.5′ long and was first noted by William Herschel in 1783. At least 43 variable stars have been observed within M4. Shining at magnitude 5.9, M4 is located at 7,200 light years away.
102mm F7 Explore Scientific FCD100 Triplet APO refractor scope,
QHY183C Cooled Cmos Color Camera, 03-07-2021
(6 x 300sec subs) 30 minute exposure total integration time.