Messier 39 (NGC 7092)
Coordinates, Gaia DR3 distance (299 pc), magnitude 4.6, A-star triangle asterism, and binocular observing guide for Messier 39 in Cygnus.
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) | 4.6 mag | ± 0.1 mag | Wide-aperture integrated photometry | definitive | Revised New General Catalogue and Index Catalogue (RNGC/IC) |
| Heliocentric distance | 975 ly | ± 10 ly | Gaia DR3 astrometric parallax of ~260 members (299 ± 3 pc) (J2016.0) | definitive | ESA Gaia Archive — Data Release 3 |
| Apparent diameter | 31 arcmin | ± 3 arcmin | Visual and Gaia DR3 member core extent | high-confidence | Revised New General Catalogue and Index Catalogue (RNGC/IC) |
| Main-sequence turnoff age | 0.28 Gyr | ± 0.03 Gyr | Gaia DR3 A0 V turnoff isochrone fitting | high-confidence | ESA Gaia Archive — Data Release 3 |
J2000 Equatorial Sky Chart & Culmination Altitude
The chart below plots Messier 39 (NGC 7092 Cygnus Open Cluster) at RA 21h 31m 47.00s, Dec +48° 26′ 20.0″ within Cygnus, 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 39 (NGC 7092) is a bright, very loose open cluster located just 975 light-years (299 ± 3 parsecs) from Earth in northeastern Cygnus. Logged by Charles Messier on October 24, 1764, and possibly noted twenty years earlier by Guillaume Le Gentil, M39 is one of the closest Messier open clusters to the Solar System, spanning 31 arcminutes across the sky—roughly the diameter of the full Moon—which corresponds to a true physical core width of only 9 light-years.
Because M39 is ~280 million years old and has a relatively modest total mass (~230 solar masses), all of its original O- and B-type stars have already evolved off the main sequence. Its surviving visual centerpiece is a striking equilateral triangle of roughly thirty brilliant white A0 to A2 main-sequence stars shining between magnitudes 6.8 and 9.5, none of which have yet expanded into red giants.
In recent Gaia DR3 kinematic surveys, astronomers traced M39's proper-motion signature far beyond its 31-arcminute classical core, uncovering leading and trailing tidal tails of low-mass F, G, and K dwarfs being sheared out by the Milky Way's differential rotation as the cluster approaches the Sun at 28 km/s.
Practical Visual Observing Guide
- Located 9° east-northeast of brilliant Deneb (α Cygni) and 2.5° north of 4th-magnitude Rho Cygni, perched at the northern end of the dark Barnard 168 dust lane.
- Visible to the naked eye at magnitude 4.6 under dark skies; because it spans 0.5° and is loosely packed, M39 is far more impressive in 7×50 or 10×50 binoculars than in high-power telescopes.
- If using a telescope, keep magnification below 30× with a wide-angle eyepiece so the crisp 25-arcminute triangle of white 7th-magnitude stars stands out against the darker background sky.
Catalog Cross-Identifications & Aliases
Common Aliases: M39 · NGC 7092
| Catalog Authority | Identifier |
|---|---|
| MESSIER | M 39 |
| NGC | NGC 7092 |
| SIMBAD | M 39 |
| WIKIDATA | Q11398 |
Related Objects, Comparisons & Guides
Messier 34 (NGC 1039 Spiral Cluster)
Coordinates, Gaia DR3 distance (507 pc), magnitude 5.2, central visual binary Otto Struve 44, and observing guide for M34 in Perseus.
North America Nebula (NGC 7000 in Cygnus)
Coordinates, Gaia DR3 distance (795 pc), Bajamar Star O3.5 III ionizer, Cygnus Wall, and wide-field observing guide for NGC 7000 in Cygnus.
Pleiades (Messier 45 Open Cluster)
Coordinates, Gaia DR3 distance (136.2 pc), magnitude 1.6, reflection nebulosity, and observing guide for the Pleiades (M45) in Taurus.
Angular Size, Separation & Field of View
How angular diameter (degrees, arcminutes, arcseconds), spherical angular separation, and small-angle physical diameter relate to telescope field of view.
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
- 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
- Revised New General Catalogue and Index Catalogue (RNGC/IC) (2024/2026 edition): Steinicke, W. 2010, Observing and Cataloguing Nebulae and Star Clusters (Cambridge Univ. Press); Verga, M. OpenNGC (CC-BY-SA 4.0 / data tables) — Wolfgang Steinicke / OpenNGC
- 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