Messier 106 (NGC 4258)
J2000 coordinates, geometric maser distance (24.7 Mly), magnitude 8.41, anomalous synchrotron arms, Seyfert 2 core, and observing guide for M106.
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) | 8.41 mag | ± 0.06 mag | Wide-field integrated CCD photometry | definitive | Revised New General Catalogue and Index Catalogue (RNGC/IC) |
| Distance in light-years | 24710000 ly | ± 360000 ly | VLBI 22-GHz H2O megamaser Keplerian geometric orbit (7.576 ± 0.112 Mpc — Reid et al. 2019) | definitive | SH0ES Local Distance Ladder Hubble Constant |
| Apparent major axis | 18.6 arcmin | ± 0.6 arcmin | Optical 25 mag/arcsec² isophotal dimensions (18.6′ × 7.2′) | definitive | Revised New General Catalogue and Index Catalogue (RNGC/IC) |
| Heliocentric recession velocity | 448 km/s | ± 2 km/s | VLBI nuclear water-maser systemic velocity & H I 21-cm disk | definitive | SIMBAD Astronomical Database (CDS) |
J2000 Equatorial Sky Chart & Culmination Altitude
The chart below plots Messier 106 (NGC 4258 Megamaser Anchor) at RA 12h 18m 57.62s, Dec +47° 18′ 13.4″ within Canes Venatici, 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
Discovered by Pierre Méchain in July 1781 and added to the Messier catalog by Helen Sawyer Hogg in 1947, Messier 106 (NGC 4258) is a giant SAB(s)bc spiral galaxy spanning ~135,000 light-years across in northern Canes Venatici. In modern precision cosmology, M106 is arguably the single most important galaxy in the sky: in 1995 radio astronomers using the Very Long Baseline Array discovered 22-gigahertz water-vapor megamasers orbiting at up to 1,000 km/s inside a razor-thin, warped molecular disk just 0.4 to 0.8 light-years from a 39.0-million-solar-mass supermassive black hole.
By comparing the centripetal Doppler acceleration of maser spots moving across our line of sight with their sub-milliarcsecond proper motions on the sky, astronomers measured a pure geometric distance to M106 of 7.576 ± 0.112 megaparsecs (24.71 million light-years) to better than 1.5% precision—allowing both the Cepheid variable period-luminosity relation and the Tip of the Red Giant Branch (TRGB) to be calibrated directly inside the same galaxy to anchor the Hubble constant (H0).
Beyond its cosmological fame, M106 exhibits two extraordinary 'anomalous spiral arms' visible in H-alpha, radio synchrotron, and Chandra X-ray images that cut at an oblique angle across the optical star-forming disk—shock-heated gas plumes driven out of the disk by relativistic jets from the active central black hole.
Practical Visual Observing Guide
- Easy star-hop: slide 7.5° southeast from Phecda (γ Ursae Majoris, the bottom-left star of the Big Dipper's bowl) toward Chara (β CVn).
- At magnitude 8.4 and 18.6′ × 7.2′ angular size, M106 is easily visible in 10×50 binoculars and any 60 mm scope.
- In a 200–300 mm telescope at 80×–140×, M106 displays a brilliant S-shaped inner lens and two sweeping spiral arcs, with the 12.0-mag edge-on companion galaxy NGC 4217 (which has its own dust lane!) sitting 40′ to the southwest.
Catalog Cross-Identifications & Aliases
Common Aliases: M106 · NGC 4258 · UGC 7353 · PGC 39600
| Catalog Authority | Identifier |
|---|---|
| MESSIER | M 106 |
| NGC | NGC 4258 |
| SIMBAD | M 106 |
| WIKIDATA | Q14362 |
Related Objects, Comparisons & Guides
Cat's Eye Galaxy (Messier 94 / NGC 4736)
J2000 coordinates, TRGB distance (15.0 Mly), magnitude 8.24, blazing inner starburst ring, outer pseudoring, and observing guide for Messier 94.
Sunflower Galaxy (Messier 63 / NGC 5055)
J2000 coordinates, TRGB distance (29.3 Mly), magnitude 8.59, flocculent spiral arms, warped H I disk, and observing guide for Messier 63 (NGC 5055).
Bode's Galaxy (Messier 81 / NGC 3031)
Coordinates, Cepheid/TRGB distance (3.63 Mpc / 11.8 Mly), magnitude 6.94, M81–M82 tidal pair, and observing guide for Bode's Galaxy in Ursa Major.
Measurement Uncertainty & Optics in Astronomy
How random vs systematic errors, asymmetric error bars, model dependencies, and optical aperture/exit-pupil limits shape astronomical measurements.
Proper Motion, Radial Velocity & Redshift
How astronomers combine tangential proper motion (mas/yr), Doppler radial velocity (km/s), and cosmological redshift (z) to reconstruct 3D space motion.
Scientific Sources & Dataset Provenance
- 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
- SH0ES Local Distance Ladder Hubble Constant (2022 Baseline Cepheid + SN Ia): Riess, A. G., et al. 2022, ApJL, 934, L7 (A Comprehensive Measurement of the Local Value of the Hubble Constant) — SH0ES Collaboration (HST / JWST)
- 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