M55 - SUMMER ROSE STAR

Messier 55 (NGC 6809), sometimes called the Summer Rose Star, is a large and loosely concentrated globular cluster located approximately 17,600 light-years from Earth in the constellation Sagittarius. It was discovered by Nicolas-Louis de Lacaille in 1752 during his observations from South Africa, and Charles Messier added it to his catalog in 1778 after multiple attempts to observe it from Paris, where its low declination made it difficult to see. M55 is one of the least concentrated globular clusters in the Messier catalog, with a Shapley-Sawyer concentration class of XI (on a scale where I is most concentrated and XII is least). This loose structure gives it a distinctly different appearance from dense globulars like M13 or M15. The cluster spans about 100 light-years in diameter and contains roughly 100,000 stars. Its relative proximity and loose structure make it one of the easiest globular clusters to resolve into individual stars with modest amateur telescopes. A 4-inch telescope under dark skies can begin to resolve stars across the face of the cluster, and an 8-inch instrument provides a spectacular view of hundreds of resolved stars. M55 is best observed during summer months from locations with a clear southern horizon, as it sits at a declination of about -31 degrees. The cluster has been an important target for stellar evolution studies because its loose structure allows individual stars to be easily measured, and its color-magnitude diagram has been extensively studied.

M55 spans approximately 100 light-years in diameter, contains roughly 100,000 stars, and lies about 17,600 light-years from Earth.