Whirlpool Galaxy (Messier 51 & NGC 5195)
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.
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) | 8.4 mag | ± 0.1 mag | Integrated CCD aperture photometry (NGC 5195 companion = 9.6 mag) | definitive | Revised New General Catalogue and Index Catalogue (RNGC/IC) |
| Extragalactic distance | 8580000 pc | ± 280000 pc | Tip of the Red Giant Branch (TRGB) + expanding photosphere of SN 2005cs & SN 2011dh (8.58 ± 0.28 Mpc) | definitive | SIMBAD Astronomical Database (CDS) |
| Apparent major axis | 11.2 arcmin | ± 0.5 arcmin | Optical isophotal dimensions (11.2′ × 6.9′) | definitive | Revised New General Catalogue and Index Catalogue (RNGC/IC) |
| Heliocentric recession velocity | 463 km/s | ± 3 km/s | H I 21-cm and optical systemic velocity | definitive | SIMBAD Astronomical Database (CDS) |
J2000 Equatorial Sky Chart & Culmination Altitude
The chart below plots Whirlpool Galaxy (Messier 51 / NGC 5194) at RA 13h 29m 52.70s, Dec +47° 11′ 42.9″ 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
The Whirlpool Galaxy (Messier 51a / NGC 5194) and its interacting dwarf companion NGC 5195 (M51b) lie 8.58 ± 0.28 megaparsecs (28.0 million light-years) away in Canes Venatici, just 3.5° southwest of Alkaid at the tip of the Big Dipper's handle. In the spring of 1845, William Parsons, the 3rd Earl of Rosse, turned his newly built 72-inch Leviathan reflector at Birr Castle in Ireland toward M51 and sketched its sweeping two-armed coil—making M51 the very first 'spiral nebula' ever discovered.
Modern hydrodynamical simulations show that M51's textbook 'grand-design' spiral structure is directly excited by tidal gravitational torques from NGC 5195, which has plunged through M51's disk twice over the past 500 million years. Those tidal density waves compress cold molecular hydrogen gas along the inner edges of the spiral arms, triggering intense bursts of massive star formation and explaining why M51 experienced three naked-eye-observatory supernovae between 1994 and 2011 (SN 1994I, SN 2005cs, and SN 2011dh).
James Webb Space Telescope NIRCam and MIRI images of M51 reveal cavernous dust bubbles blown out by young stellar clusters and intricate polycyclic aromatic hydrocarbon filaments threading the spiral lanes.
Practical Visual Observing Guide
- Sweep 3.5° southwest from Alkaid (η Ursae Majoris) to locate the pair.
- In 10×50 binoculars or a 70–100 mm telescope at 50×–80×, M51 and NGC 5195 appear as two distinct, touching round glows—a big nucleus and a smaller northern knot.
- Under dark Bortle 1–3 skies, a 200–250 mm (8–10 inch) telescope at 100×–150× begins to trace the two winding spiral arcs and the luminous tidal bridge connecting M51's outer arm to NGC 5195.
Catalog Cross-Identifications & Aliases
Common Aliases: M51 · NGC 5194 · NGC 5195 · Rosse's Question Mark
| Catalog Authority | Identifier |
|---|---|
| MESSIER | M 51 |
| NGC | NGC 5194 |
| SIMBAD | M 51 |
| WIKIDATA | Q13957 |
Related Objects, Comparisons & Guides
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Spring Galaxy Season: Ursa Major to Virgo
Spring galaxy observing guide from Ursa Major (M81, M82, Whirlpool M51) across Coma/Virgo to giant elliptical M87, the Sombrero Galaxy (M104), and 3C 273.
Small-Telescope Messier Objects Tour (80–150mm)
Curated seasonal tour of flagship Messier clusters, nebulae, and galaxies optimized for 80 mm to 150 mm (3-inch to 6-inch) refractors and reflectors.
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.
Astronomical Catalogs Explained (M, NGC, Gaia)
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Messier Catalog (M) Objects & Cross-Reference
Guide and cross-walk to Charles Messier's flagship deep-sky catalog (M1 to M104 in FastAstro), linking Messier numbers to NGC IDs, distances, and magnitudes.
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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
- 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
- JWST / MAST Science Archive & Mission Documentation (Cycle 1–4 Public Releases (2022–2026)): Rigby, J., et al. 2023, PASP, 135, 048001 (The Science Performance of JWST as Characterized in Commissioning) — NASA / ESA / CSA / STScI