Messier 22 (Great Sagittarius Cluster / NGC 6656)
Coordinates, Gaia DR3 distance (3.30 kpc), magnitude 5.10, stellar-mass black holes, and observing guide for Messier 22 in Sagittarius.
Provenance-Backed Scientific Measurements
Every measurement below preserves its unit, uncertainty interval, observational method, reference epoch, quality status, and primary catalog source. See Uncertainty & Provenance for how competing measurements are handled.
| Parameter | Value | Uncertainty | Method & Epoch | Quality Status | Source Archive |
|---|---|---|---|---|---|
| Integrated visual magnitude (V) | 5.1 mag | ± 0.05 mag | Wide-aperture integrated photometry | definitive | Catalog of Parameters for Milky Way Globular Clusters |
| Heliocentric distance | 10760 ly | ± 130 ly | Gaia EDR3 parallax + HST proper motions (3.30 ± 0.04 kpc) (J2016.0) | definitive | ESA Gaia Archive — Data Release 3 |
| Apparent tidal diameter | 32 arcmin | ± 2 arcmin | Deep radial surface-density profile | high-confidence | Revised New General Catalogue and Index Catalogue (RNGC/IC) |
| Main-sequence turnoff age | 12.6 Gyr | ± 0.5 Gyr | HST ACS multi-population CMD fitting | model-dependent | Catalog of Parameters for Milky Way Globular Clusters |
J2000 Equatorial Sky Chart & Culmination Altitude
The chart below plots Messier 22 (NGC 6656 Sagittarius Cluster) at RA 18h 36m 23.94s, Dec -23° 54′ 17.1″ within Sagittarius, alongside peak meridian transit altitudes for 40°N and 30°S observers. Use the RA/Dec Coordinate Converter to compute exact culmination altitude for your latitude.
Astrophysical Context & Structure
Messier 22 (NGC 6656, the Great Sagittarius Cluster) is the brightest globular cluster in the entire Messier catalog and the third brightest in the whole sky, surpassed only by southern showpieces Omega Centauri and 47 Tucanae. First recorded by German astronomer Abraham Ihle on August 26, 1665—making it the very first globular cluster ever discovered—M22 lies just 10,760 light-years (3.30 ± 0.04 kiloparsecs) away in front of the rich Sagittarius star cloud.
Spanning 32 arcminutes across on the sky (larger than the full Moon) and roughly 100 light-years in physical diameter, M22 contains ~480,000 solar masses of stars. Like Omega Centauri, M22 exhibits two chemically distinct stellar populations differing in iron, calcium, and s-process abundances, pointing to extended chemical self-enrichment or a merger of two ancient protoclusters.
In 2012, deep radio continuum observations with the Karl G. Jansky Very Large Array discovered two flat-spectrum radio sources (M22-VLA1 and M22-VLA2) in M22's core—the first stellar-mass black holes (10–20 solar masses each) ever detected inside a Milky Way globular cluster, proving that dynamical kicks do not always eject all black holes during cluster evolution. M22 also hosts the rare hydrogen-poor planetary nebula IRAS 18333−2357.
Practical Visual Observing Guide
- Exceptionally easy to find just 2.4° northeast of Kaus Borealis (λ Sagittarii), the top star of the Sagittarius Teapot lid.
- At magnitude 5.10, M22 is outshone by M13 only at high northern latitudes where M22 sits low in horizon haze; from latitudes south of 40°N it is an easy naked-eye knot and larger than M13 in binoculars.
- Because its brightest red giants reach magnitude 10.7, even a 70–100 mm telescope at 60×–100× resolves hundreds of golden-orange and blue stars across an elliptical core.
Catalog Cross-Identifications & Aliases
Common Aliases: M22 · NGC 6656 · Great Sagittarius Cluster
| Catalog Authority | Identifier |
|---|---|
| MESSIER | M 22 |
| NGC | NGC 6656 |
| SIMBAD | M 22 |
| WIKIDATA | Q11367 |
Related Objects, Comparisons & Guides
Messier 28 (NGC 6626 Pulsar Cluster)
Coordinates, Gaia DR3 distance (5.37 kpc), magnitude 6.79, first globular millisecond pulsar PSR B1821-24, and observing guide for M28 in Sagittarius.
Omega Centauri (NGC 5139 Cluster)
Coordinates, Gaia DR3 distance (5.43 kpc), magnitude 3.68, and multi-population core data for Omega Centauri (NGC 5139) in Centaurus.
Messier 13 (Hercules Globular Cluster)
Coordinates, Gaia DR3 distance (7.42 kpc), visual magnitude 5.78, and Keystone finder guide for Messier 13 (NGC 6205) in Hercules.
Apparent vs Absolute Magnitude Explained
Understand the logarithmic Pogson astronomical magnitude scale, apparent visual magnitude (m), absolute magnitude (M at 10 parsecs), and bolometric corrections.
Trigonometric Parallax, Parsecs & Gaia DR3
How trigonometric parallax (d_pc = 1 / p_arcsec), the distance modulus equation, Hipparcos, and Gaia DR3 microarcsecond astrometry measure cosmic distances.
Scientific Sources & Dataset Provenance
- Catalog of Parameters for Milky Way Globular Clusters (2010 / 2021 Gaia EDR3 revision): Harris, W. E. 1996 (2010 ed.), AJ, 112, 1487; Vasiliev, E. & Baumgardt, H. 2021, MNRAS, 505, 5978 — McMaster University / Gaia EDR3 Cluster Survey
- ESA Gaia Archive — Data Release 3 (DR3 (2022-06-13)): Gaia Collaboration, Vallenari, A., et al. 2023, A&A, 674, A1 (Gaia Data Release 3) — European Space Agency / Gaia DPAC
- SIMBAD Astronomical Database (CDS) (2026-10 release): Wenger, M., et al. 2000, A&AS, 143, 9 (The SIMBAD astronomical database) — Centre de Données astronomiques de Strasbourg