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Messier catalogue · Open cluster

M21 NGC 6531

Cluster next to M20.

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Photograph of M21 — NGC 6531
Photograph from volume II · The field may be partial and the colours may result from processing. Credits and source.

Essential information

Category
Open cluster
Constellation
Sagittarius (Sgr)
Alternative designation
NGC 6531
Right ascension / declination
18h05 / −22°30′
Visual magnitude
5,9
Indicative distance
≈ 3 800 al

RA / Dec.: J2000, rounded to the nearest minute. ly = light-year; M ly = million light-years; ≈ = approximate value; — = not available.

At the eyepiece

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Cluster next to M20.

Locating guide from the book1,6° NE of 4 Sgr

N, S, E and W indicate cardinal directions; combinations give a more precise direction. Greek letters identify the constellation’s guide stars. Check the route on a suitable chart.

Photographs help you recognise structures, but do not predict the view through an eyepiece. Detection depends on the sky, the object’s altitude and your instrument.

Sources and credits

Fact sheet adapted from Comprendre comment explorer le ciel, volume II by Steve Cimolino, version dated 17 October 2026. Values and advice are taken from the book; they are not real-time ephemerides.

RubinObs/NOIRLab/SLAC/NSF/DOE/AURA. CC BY 4.0.

Photograph source and original description ↗ · CC BY 4.0

Image resized and converted to WebP for this site; colours and proportions retained. Each image’s own licence continues to apply.

Book data: NASA HEASARC ; coordinates adapted fromOpenNGC, Mattia Verga under CC BY-SA 4.0. The relevant adapted data retain this licence. All image attributions and terms →

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