Messier 46 (NGC 2437)
Coordinates, Gaia DR3 distance (1.51 kpc), magnitude 6.1, superposed planetary nebula NGC 2438, and observing guide for M46 in Puppis.
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) | 6.1 mag | ± 0.1 mag | Wide-aperture integrated photometry | definitive | Revised New General Catalogue and Index Catalogue (RNGC/IC) |
| Heliocentric distance | 4925 ly | ± 100 ly | Gaia DR3 astrometric parallax of ~1,900 members (1.51 ± 0.03 kpc) (J2016.0) | definitive | ESA Gaia Archive — Data Release 3 |
| Apparent diameter | 27 arcmin | ± 2 arcmin | Member star-count boundary | high-confidence | Revised New General Catalogue and Index Catalogue (RNGC/IC) |
| Main-sequence turnoff age | 0.25 Gyr | ± 0.03 Gyr | Gaia DR3 A0 V turnoff & red-clump isochrone fitting | high-confidence | ESA Gaia Archive — Data Release 3 |
J2000 Equatorial Sky Chart & Culmination Altitude
The chart below plots Messier 46 (NGC 2437 & NGC 2438 Planetary Pair) at RA 07h 41m 48.00s, Dec -14° 48′ 36.0″ within Puppis, 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 46 (NGC 2437) is a rich, finely powdered open cluster located 4,925 light-years (1.51 ± 0.03 kiloparsecs) away in northern Puppis, forming a famous winter binocular double with the much closer, coarser cluster M47 just 1.3 degrees to the west. Discovered by Charles Messier on February 19, 1771—only three days after he published the first edition of his catalog—M46 spans 27 arcminutes (~39 light-years physically) and contains nearly 2,000 gravitationally bound stars.
What makes M46 one of the most celebrated deep-sky targets in the entire sky is the 10.8-magnitude planetary nebula NGC 2438 sitting 7 arcminutes north-northeast of the cluster's center. Discovered by William Herschel in 1786, NGC 2438 looks like a miniature 66-arcsecond smoke ring floating right among M46's glittering 10th-to-13th magnitude A-type stars. However, Doppler spectroscopy and Gaia astrometry show that NGC 2438 is receding at +77 km/s compared to M46's +48 km/s—proving the planetary nebula is a chance line-of-sight alignment.
Remarkably, M46 also hosts a second, genuinely bound bipolar protoplanetary nebula—the 'Calabash' or 'Rotten Egg' Nebula (OH 231.8+4.2)—erupting from the symbiotic Mira variable star QX Puppis on the cluster's outskirts.
Practical Visual Observing Guide
- Located 5° east of Alpha Monocerotis and 1.3° east-southeast of naked-eye cluster M47 in northern Puppis.
- In 10×50 binoculars M46 and M47 sit side by side: M47 resolves into bright, coarse stars, whereas M46 glows as a smooth, misty 6.1-magnitude ball.
- In a 150–250 mm telescope at 80×–150× (especially with a UHC or O-III filter), M46 resolves into over 150 uniform 11th-magnitude stars with the ghostly annular disk of planetary nebula NGC 2438 floating in its northern quadrant.
Catalog Cross-Identifications & Aliases
Common Aliases: M46 · NGC 2437
| Catalog Authority | Identifier |
|---|---|
| MESSIER | M 46 |
| NGC | NGC 2437 |
| SIMBAD | M 46 |
| WIKIDATA | Q11413 |
Related Objects, Comparisons & Guides
Messier 47 (NGC 2422 Puppis Open Cluster)
Coordinates, Gaia DR3 distance (475 pc), magnitude 4.2, Messier sign-error history, and observing guide for Messier 47 in Puppis.
Messier 37 (NGC 2099 Salt-and-Pepper Cluster)
Coordinates, Gaia DR3 distance (1.42 kpc), magnitude 5.6, central red giant HD 250068, and observing guide for Messier 37 in Auriga.
Ring Nebula (Messier 57 in Lyra)
Coordinates, Gaia DR3 central star distance (787 pc), magnitude 8.8, and telescope observing guide for the Ring Nebula (M57) in Lyra.
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.
Surface Brightness & Extended Objects Guide
Why surface brightness (mag/arcsec²) governs nebula and galaxy visibility more than integrated magnitude, and how exit pupil controls eyepiece contrast.
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