Globular Cluster Messier 55

Messier 55
Messier 55: Infrared image with the VISTA telescope of the ESO observatory on the Paranal in Chile [279]


M 55 is a large, but rather loose globular cluster. It was discovered by Nicolas Lacaille in 1751 when he was staying at the Cape of Good Hope in South Africa to map the southern starry sky. He described it as the «shadowy nucleus of a large comet». Charles Messier confirmed its existence in the summer of 1778. He noted: «A nebula that is a whitish spot and extends 6' all around. The light is even and does not seem to contain a star.» He seems to have searched for it as early as 1764, without success. The Herschels were able to resolve the globular cluster into single stars with their large reflector telescope. [4]

Physical Properties

The distance from M 55 is about 5.4 kpc (17'600 light years) and it is moving away at 174 km/s. The globular cluster contains around 269'000 times the mass of our sun. [145, 251]

«Revised New General Catalogue and Index Catalogue» Dr. Wolfgang Steinicke, 2021 [277]
DesignationNGC 6809
TypeGCL (XI)
Right Ascension19h 39m 59.4s
Declination-30° 57' 42"
Diameter19.00 arcmin
Visual magnitude6.3 mag
Dreyer Descriptionglobular, pB, L, R, vRi, vgbM, st 12…15
IdentificationM 55, GCL 113, ESO 460-SC21

Finder Chart

M 55 is located in the eastern part of the constellation Sagittarius, about 7° east and slightly south of the star Ascella (ζ Sagittarii). Due to its southern position of -30° declination, it does not come very far over the southern horizon. It is best seen in the months of June to August.

Chart Messier 55
Chart created using SkySafari 6 Pro and STScI Digitized Sky Survey. [149, 160]


4«Burnham's Celestial Handbook: An Observer's Guide to the Universe Beyond the Solar System» by Robert Burnham; Dover Publications, Inc.; Voume I: ISBN 0-486-23567-X; Volume II: ISBN 0-486-23568-8; Volume III: ISBN 0-486-23673-0
145SIMBAD astronomical database;
149SkySafari 6 Pro, Simulation Curriculum;
160The STScI Digitized Sky Survey;
251«Young Radio Pulsars in Galactic Globular Clusters» Jason Boyles, Duncan R. Lorimer, Phil J. Turk, Robert Mnatsakanov, Ryan S. Lynch, Scott M. Ransom, Paulo C. Freire, Khris Belczynski; The Astrophysical Journal, Volume 742, Number 1; DOI:10.1088/0004-637X/742/1/51
277«Historische Deep-Sky Kataloge» von Dr. Wolfgang Steinicke; (2021-02-17)
279VISTA infrared image of the globular star cluster Messier 55; (2021-02-19)