NGC 6553 is a

globular cluster A globular cluster is a spheroidal conglomeration of stars. Globular clusters are bound together by gravity, with a higher concentration of stars towards their centers. They can contain anywhere from tens of thousands to many millions of membe ...

in the

constellation A constellation is an area on the celestial sphere in which a group of visible stars forms Asterism (astronomy), a perceived pattern or outline, typically representing an animal, mythological subject, or inanimate object. The origins of the e ...

Sagittarius. NGC 6553 has an

apparent magnitude Apparent magnitude () is a measure of the brightness of a star or other astronomical object observed from Earth. An object's apparent magnitude depends on its intrinsic luminosity, its distance from Earth, and any extinction of the object's li ...

of about 8th magnitude with an apparent diameter of 8.2 arcminutes. Its

Shapley–Sawyer Concentration Class The Shapley–Sawyer Concentration Class is a classification system on a scale of one to twelve using Roman numerals for globular clusters according to their concentration. The most highly concentrated clusters such as M75 are classified as Class I ...

is XI, meaning the star concentration is very loose even at the center; it has stars of magnitude 20 and dimmer. It is located just over a degree southeast of

Messier 8 Messier may refer to: People with the surname *Charles Messier, French astronomer *Éric Messier, former NHL defenseman *George Messier, French inventor *Jean-Marie Messier, former CEO of Vivendi Universal *Marc Messier, Canadian actor from Quebec ...

, the Lagoon Nebula. Unlike common

s, NGC 6553 is relatively metal-rich, and there is evidence of at least two periods of star formation. Due to a complex star-forming record, the stars in the cluster are differing in composition, most notably in concentrations of

sodium Sodium is a chemical element with the symbol Na (from Latin ''natrium'') and atomic number 11. It is a soft, silvery-white, highly reactive metal. Sodium is an alkali metal, being in group 1 of the periodic table. Its only stable iso ...

and

aluminium Aluminium (aluminum in American and Canadian English) is a chemical element with the symbol Al and atomic number 13. Aluminium has a density lower than those of other common metals, at approximately one third that of steel. I ...

. NGC 6553 is very similar in composition to

NGC 6528 NGC 6528 is a globular cluster in the constellation Sagittarius, and is listed in the New General Catalogue. It has an apparent magnitude of about 11 and a diameter of about 16 arcminutes, and its Shapley-Sawyer Concentration Class is V, contain ...

, suggesting an origin in a similar environment.

References

External links

*
NGC 6553
Globular clusters Sagittarius (constellation) 6553 {{star-cluster-stub