Messier 55

Messier 55 is a globular cluster in the constellation of Sagittarius, located 17.600 light-years away. Being discovered by Nicolas Louis de Lacaille in 1752 from South Africa, this cluster has proven to be hard to observe from Paris, where Charles Messier tried for 22 years to see and catalog it. The difficulty was a consequence of the fact that M 55 never rises more than 11° in the night sky at Paris’s location. Sometimes, it is known as Summer Rose Cluster.
This cluster has a mass of 270.000 Suns and a low metallicity, given the age of it – approximately 12,5 billion years old. It has an apparent magnitude of +6,3 and can be seen even in a 50mm binoculars. It is 100 light-years wide and here we can find 55 variable stars. Messier 55 doesn’t have a very rich core and the stellar density is lower overall, compared to other globular clusters, most likely because of the gravitational interactions with our Milky Way. Moreover, the cluster is rich in “blue stragglers”, which are “reinvigorated” stars born from the collision of older stars in the cluster.