Messier 55 (also M55, NGC 6809 and GCL 113) is a magnitude +7.42 globular star cluster located 17,600 light-years away in the constellation Sagittarius.
The cluster was discovered by French astronomer Nicolas Louis de Lacaille using a 1.27 cm (0.5 inch) 8x refractor in Table Bay, South Africa on the 16th June 1752. The cluster was observed by Charles Messier in Paris, France on the 24th July 1778, and listed as number 55 in his catalogue of comet-like objects.
Right Ascension 19h 39m 59.71s, Declination -30° 57' 53.1"
The cluster can be seen with a pair of 50 mm binoculars, although resolving the individual stars requires a medium-sized telescope. Read more
A new image of Messier 55 from ESO's VISTA infrared survey telescope shows tens of thousands of stars crowded together like a swarm of bees. Besides being packed into a relatively small space, these stars are also among the oldest in the Universe. Astronomers study Messier 55 and other ancient objects like it, called globular clusters, to learn how galaxies evolve and stars age. Globular clusters are held together in a tight spherical shape by gravity. In Messier 55, the stars certainly do keep close company: approximately one hundred thousand stars are packed within a sphere with a diameter of only about 25 times the distance between the Sun and the nearest star system, Alpha Centauri. Read more