M55 - The Summer Rose Star
M55, also known as the Summer Rose Star, is a globular cluster located in the constellation Sagittarius.
The cluster has an apparent magnitude of 7.42 and lies at a distance of 17,600 light years from Earth. It has the designation NGC 6809 in the New General Catalogue. Messier 55 occupies 19 arc minutes of apparent sky, which is almost two thirds the size of the full Moon.
The cluster has a linear diameter of almost 100 light years. It can be seen in 50 mm binoculars, but can only be resolved in medium-sized and larger telescopes. 8-inch telescopes will easily resolve many of the cluster’s stars.
Messier 55 has a mass about 269,000 times that of the Sun. It contains roughly 100,000 stars. Only 55 variables have been detected in the cluster’s central region. The stars in the cluster are mostly old and red, but M55 also contains an unusually high number of blue stragglers, old stars that appear younger, bluer and more luminous than similar stars their age as a result of interactions and mergers with neighbouring stars in the cluster.
Facts about M55 by Keith Turnecliff
The cluster is located 34,000 light-years from Earth in the constellation Canes Venatici. It has an apparent magnitude of 6.2 and can be spotted using a pair of binoculars.