Open cluster · Sagittarius

M21

Also known as: NGC 6531

mag 5.913′ across

About

M21 is an open cluster of magnitude 5.9 in Sagittarius, about 13′ across.

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How to find it

  • M21 is in the constellation Sagittarius.
  • Best evenings: around early August it is highest at about 9 pm (10 pm in summer time); a month earlier, two hours later.
  • Where on Earth: it is seen well, at least 10° up, from south of 58° N.

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When it rises and sets tonight, how high it climbs and how much the Moon gets in the way are worked out in your browser for your place.

What you will see

  • EyesA faint smudge at the limit of vision, only from a dark site.
  • Binoculars (10×50)A small knot of stars, partly resolved.
  • Telescope (6–8 inch)Dozens of stars, many sharp and some coloured.

For a dark country sky with no Moon. From a city, faint galaxies and nebulae can disappear completely.

Facts

DesignationsM21, NGC 6531
TypeOpen cluster
Magnitude5.9The smaller the number, the brighter.
Apparent size13′the full Moon is 31′ across
ConstellationSagittarius
Right ascension (J2000)18h 04m 13.4s
Declination (J2000)−22° 29′ 24″

More in Sagittarius

M24Small Sagittarius Star CloudOther · mag 4.5M25Open clustermag 4.6M22Great Sagittarius ClusterGlobular cluster · mag 5.1M23Open clustermag 5.5M8Lagoon NebulaEmission nebula · mag 5.8M18Open clustermag 6.9M28Globular clustermag 6.9M17Omega NebulaEmission nebula · mag 7.0
All NGC objects in Sagittarius →Sagittarius on the constellations page →

Sources and credits

Catalog data: OpenNGC by Mattia Verga, CC BY-SA 4.0, and d3-celestial by Olaf Frohn, BSD 3-Clause. All data sources →