Messier 55

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title: "Messier 55" type: doc version: 1 created: 2026-02-28 author: "Wikipedia contributors" status: active scope: public tags: ["carina–sagittarius-arm", "globular-clusters", "sagittarius-(constellation)", "messier-objects", "ngc-objects", "astronomical-objects-discovered-in-1752"] description: "Globular cluster in the constellation Sagittarius" topic_path: "general/carina-sagittarius-arm" source: "https://en.wikipedia.org/wiki/Messier_55" license: "CC BY-SA 4.0" wikipedia_page_id: 0 wikipedia_revision_id: 0

::summary Globular cluster in the constellation Sagittarius ::

::data[format=table title="Infobox globular cluster"]

Field	Value
name	Messier 55
image	[[File:Messier 55 VISTA.jpg
caption	Globular cluster Messier 55 in Sagittarius
epoch	J2000
class	XI
constellation	Sagittarius
ra
dec
dist_ly	17.6 kly
appmag_v	6.3
size_v	19.0
mass_msol
radius_ly	48 ly
metal_fe	–1.94
age	12.3 Gyr
names	M55, NGC 6809, GCl 113, C 1936-310
::

| name = Messier 55 | image = [[File:Messier 55 VISTA.jpg|300px]] | caption = Globular cluster Messier 55 in Sagittarius | credit = | epoch = J2000 | class = XI | constellation = Sagittarius | ra = | dec = | dist_ly = 17.6 kly | dist_pc = | appmag_v = 6.3 | size_v = 19.0 | mass_msol = | radius_ly = 48 ly | metal_fe = –1.94 | v_hb = | age = 12.3 Gyr | notes = | names = M55, NGC 6809, GCl 113, C 1936-310 Messier 55 (also known as M55, NGC 6809, or Specter Cluster) is a globular cluster in the south of the constellation Sagittarius. It was discovered by Nicolas Louis de Lacaille in 1752 while observing from what today is South Africa. Starting in 1754, Charles Messier made several attempts to find this object from Paris but its low declination meant from there it rises daily very little above the horizon, hampering observation. He observed and catalogued it in 1778. The cluster can be seen with 50 mm binoculars; resolving individual stars needs a medium-sized telescope.

It is about 17,600 light-years away from Earth. It contains about 269,000 solar masses (). As with other Milky Way globular clusters, it has few elements other than hydrogen and helium compared to the Sun. Messier 55 therefore has "low metallicity". This quantity is normally listed as the base 10 logarithm of the proportion of the Sun; for NGC 6809 the metallicity is given by: [Fe/H] = −1.94 dex, whereby −2 would be 100 times less iron than the Sun. This means the cluster has 1.1% of the proportion of the Sun's iron compared to hydrogen and helium.

Only about 55 variable stars have been found in the central part of M55.

Gallery

|File:M55HunterWilson.jpg|Messier 55, wide field view |File:M55map.png|Map showing the location of M55

References and footnotes

References

1. "Messier 55".
2. From [[trigonometry]]: radius = {{nowrap|distance × sin( diameter_angle / 2 )}} = {{nowrap|17,600 × sin(19{{prime}}/2)}} = 48.6 ly.
3. "M 55".
4. (November 2011). "Young Radio Pulsars in Galactic Globular Clusters". The Astrophysical Journal.
5. (2007). "Illustrated guide to astronomical wonders". [[O'Reilly Media, Inc.]].
6. (December 2010). "The ACS Survey of Galactic Globular Clusters. X. New Determinations of Centers for 65 Clusters". The Astronomical Journal.
7. (September 2010). "The Cluster AgeS Experiment (CASE). Variable Stars in the Globular Cluster M55". Acta Astronomica.
8. (August 1927). "A Classification of Globular Clusters". Harvard College Observatory Bulletin.
9. (April 2008). "The correlation between blue straggler and binary fractions in the core of Galactic globular clusters". Astronomy and Astrophysics.

::callout[type=info title="Wikipedia Source"] This article was imported from Wikipedia and is available under the Creative Commons Attribution-ShareAlike 4.0 License. Content has been adapted to SurfDoc format. Original contributors can be found on the article history page. ::