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Open star cluster

Messier 21

Also M21 · NGC 6531

Open in OuranosCompare its size

An open cluster: a family of stars born together from one cloud, slowly drifting apart.

Measured

Distance
3,920 light-years
Size
about 10.6 light-years across (approximate)
Constellation
Sagittarius
Position (J2000)
RA 18h 04m 10s, Dec −22.50°

How far, from the Sun

3,920 light-years. To cross it:

  • Light3,920 years
  • Voyager 1's speed69.7 million years
  • Driving at 100 km/h42.3 billion years

Voyager 1 at the speed it moved outward over the year to 2026-10-25 (JPL Horizons). Driving: nonstop, never refuelling.

Facts

  • It sits just north of the Trifid Nebula (M20), about half a degree away, and is probably between about 5 and 13 million years old.
  • Gaia picks out about 212 member stars (Hunt & Reffert 2023).

Where this comes from

  • Hunt & Reffert 2023, A&A 673, A114: Gaia DR3 cluster distance 1201.8 pc (16th–84th percentile 1198.9–1204.7 pc)
  • This research has made use of the SIMBAD database, CDS, Strasbourg, France (Wenger et al. 2000, A&AS 143, 9).
  • This research has made use of the VizieR catalogue access tool, CDS, Strasbourg, France (DOI: 10.26093/cds/vizier).

Every catalogue Ouranos draws is credited on the credits page.