Fireworks Galaxy (NGC 6946 / Arp 29 / Caldwell 12)
J2000 coordinates, TRGB distance (25.2 Mly), magnitude 9.60, ten recorded supernovae, BH1 direct-collapse candidate, and NGC 6946 observing guide.
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) | 9.6 mag | ± 0.1 mag | Integrated CCD aperture photometry (dimmed by ~1.1 mag of foreground Milky Way dust) | definitive | Revised New General Catalogue and Index Catalogue (RNGC/IC) |
| Distance in light-years | 25200000 ly | ± 800000 ly | HST Tip of the Red Giant Branch (TRGB: 7.72 ± 0.25 Mpc — Anand et al. 2018) | definitive | SH0ES Local Distance Ladder Hubble Constant |
| Apparent major axis | 11.5 arcmin | ± 0.5 arcmin | Optical isophotal dimensions (11.5′ × 9.8′) | definitive | Revised New General Catalogue and Index Catalogue (RNGC/IC) |
| Heliocentric recession velocity | 40 km/s | ± 2 km/s | THINGS H I 21-cm synthesis velocity field | definitive | SIMBAD Astronomical Database (CDS) |
J2000 Equatorial Sky Chart & Culmination Altitude
The chart below plots Fireworks Galaxy (NGC 6946 / Caldwell 12) at RA 20h 34m 52.33s, Dec +60° 09′ 13.3″ 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
Discovered by William Herschel on September 9, 1798, on the exact border of Cygnus and Cepheus, NGC 6946 (Caldwell 12, Arp 29) has earned the title of the Fireworks Galaxy by holding the all-time astronomical record for the most supernovae observed in any single galaxy: ten confirmed supernovae in exactly 100 years (SN 1917A, 1939C, 1948B, 1968D, 1969P, 1980K, 2002hh, 2004et, 2008S, and 2017eaw)! Even though our Milky Way contains roughly twice as many stars as NGC 6946, the Fireworks Galaxy converts cold molecular gas into massive short-lived OB stars at nearly ten times the specific rate per unit area.
Because NGC 6946 lies just 11.7 degrees north of the Milky Way's galactic plane, our view of this 25.2-million-light-year-distant face-on spiral looks directly through a veil of foreground Galactic stars and ~1.1 magnitudes of interstellar dust—without which NGC 6946 would shine at magnitude 8.5 as one of the brightest spirals in the northern sky.
In 2009 astronomers using the Large Binocular Telescope and Hubble Space Telescope witnessed an unprecedented event in NGC 6946: a 25-solar-mass red supergiant star (N6946-BH1) brightened briefly in 2009 and then vanished completely in optical light without exploding as a supernova—becoming the strongest observational candidate for a 'failed supernova' collapsing directly into a stellar-mass black hole.
Practical Visual Observing Guide
- Located 2° southwest of Eta Cephei (η Cep) right on the Cygnus–Cepheus border.
- Sitting just 38 arcminutes northwest of NGC 6946 is the rich 6th-magnitude Milky Way open star cluster NGC 6939—allowing wide-field eyepieces (30×–60×) to frame a foreground star cluster and a background spiral galaxy side by side.
- Because foreground extinction dims NGC 6946's 11.5′ face-on disk, use a 200–350 mm telescope under dark skies at 80×–140× to trace its four broad spiral arms (especially the heavy northeastern arm cataloged as Arp 29).
Catalog Cross-Identifications & Aliases
Common Aliases: NGC 6946 · Fireworks Galaxy · Arp 29 · Caldwell 12 · UGC 11597
| Catalog Authority | Identifier |
|---|---|
| NGC | NGC 6946 |
| SIMBAD | NGC 6946 |
| WIKIDATA | Q500501 |
Related Objects, Comparisons & Guides
Pinwheel Galaxy (Messier 101 / NGC 5457)
J2000 coordinates, Cepheid/TRGB distance (21.6 Mly), magnitude 7.86, giant H II regions, SN 2011fe & SN 2023ixf, and observing guide for M101.
Messier 61 (NGC 4303 Supernova-Rich Spiral)
J2000 coordinates, distance (52.5 Mly), magnitude 9.65, nuclear starburst ring, eight recorded supernovae, and observing guide for Messier 61.
Phantom Galaxy (Messier 74 / NGC 628)
J2000 coordinates, TRGB/SN distance (31.9 Mly), magnitude 9.46, face-on grand-design spiral arms, JWST dust filaments, and observing guide for M74.
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.
Bortle Dark-Sky Scale & Sky Brightness Guide
Reference guide to the 9-class Bortle Dark-Sky Scale, zenith Sky Quality Meter (SQM) readings in mag/arcsec², naked-eye limiting magnitude, and light pollution.
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