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.
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) | 7.86 mag | ± 0.08 mag | Wide-field integrated CCD photometry | definitive | Revised New General Catalogue and Index Catalogue (RNGC/IC) |
| Distance in light-years | 21600000 ly | ± 600000 ly | SH0ES HST/JWST Cepheids + Tip of the Red Giant Branch (6.64 ± 0.18 Mpc) | definitive | SH0ES Local Distance Ladder Hubble Constant |
| Apparent major axis | 28.8 arcmin | ± 1 arcmin | Optical 25 mag/arcsec² isophotal dimensions (28.8′ × 26.9′ — nearly full Moon size) | definitive | Revised New General Catalogue and Index Catalogue (RNGC/IC) |
| Heliocentric recession velocity | 241 km/s | ± 2 km/s | H I 21-cm synthesis velocity field | definitive | SIMBAD Astronomical Database (CDS) |
J2000 Equatorial Sky Chart & Culmination Altitude
The chart below plots Pinwheel Galaxy (Messier 101 / NGC 5457) at RA 14h 03m 12.58s, Dec +54° 20′ 55.5″ within Ursa Major, 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 on March 27, 1781, the Pinwheel Galaxy (Messier 101, NGC 5457) is a colossal face-on SAB(rs)cd spiral galaxy situated 21.6 million light-years away above the handle of the Big Dipper in Ursa Major. Spanning nearly 29 arcminutes on the sky—almost the exact angular diameter of the full Moon—M101 measures ~170,000 light-years across and contains roughly one trillion stars, making it comparable in physical size to the Andromeda Galaxy.
Halton Arp cataloged M101 as Arp 26 ('Spiral with One Heavy Arm') because gravitational tidal interactions with its dwarf companions (NGC 5474, NGC 5477, and NGC 5204) have pulled its eastern spiral arms closer to the core while stretching its western arms far outward. Studded along those arms are over 1,200 H II star-forming nebulae, eleven of which are so enormous and luminous that William Herschel and John Dreyer gave them their own independent NGC numbers (including the monster H II complex NGC 5461, NGC 5462, and NGC 5471).
In modern astrophysics M101 hosted two of the most intensively studied supernovae in history: SN 2011fe (August 2011), a pristine Type Ia thermonuclear explosion that peaked at magnitude 9.9 (visible in 50 mm binoculars!), and SN 2023ixf (May 2023), a Type II core-collapse explosion near NGC 5461 that reached magnitude 10.8 as the closest core-collapse supernova of the 21st century.
Practical Visual Observing Guide
- Forms an equilateral triangle (5.5° on a side) north-northeast of Mizar (ζ UMa) and Alkaid (η UMa) at the end of the Big Dipper's handle; star-hop along a curving chain of four 7th-magnitude stars leading straight to M101.
- Because its 7.86-magnitude light is spread over a 28.8′ × 26.9′ disk, M101 has a low surface brightness (~23.8 mag/arcsec²): use 10×50 binoculars or a wide-field eyepiece (25×–50×) under dark skies first.
- In a 250–400 mm (10–16 inch) telescope at 100×–180× (especially with a UHC nebula filter), you can resolve multiple individual NGC H II regions—NGC 5461 (mag 12.8), NGC 5462, NGC 5450, and NGC 5471—glowing like tiny nebulae along M101's spiral arms!
Catalog Cross-Identifications & Aliases
Common Aliases: M101 · NGC 5457 · UGC 8981 · Arp 26 · Pinwheel Galaxy
| Catalog Authority | Identifier |
|---|---|
| MESSIER | M 101 |
| NGC | NGC 5457 |
| SIMBAD | M 101 |
| WIKIDATA | Q14351 |
Related Objects, Comparisons & Guides
Whirlpool Galaxy (Messier 51 / NGC 5194)
Coordinates, SN II-P / TRGB distance (8.58 Mpc / 28.0 Mly), grand-design spiral arms, NGC 5195 tidal companion, and observing guide for M51.
Triangulum Galaxy (Messier 33 / NGC 598)
Coordinates, Cepheid/maser distance (859 kpc / 2.80 Mly), low surface brightness (23.0 mag/arcsec²), NGC 604 H II region, and observing guide for M33.
Southern Pinwheel (Messier 83 / NGC 5236)
J2000 coordinates, Cepheid/TRGB distance (15.2 Mly), magnitude 7.54, barred spiral starburst core, six supernovae, and observing guide for Messier 83.
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