Coma Pinwheel Galaxy (Messier 99 / NGC 4254)
J2000 coordinates, Tully-Fisher distance (49.6 Mly), magnitude 9.86, asymmetric one-armed spiral, VIRGOHI21 gas tail, and observing guide for M99.
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) | 9.86 mag | ± 0.1 mag | Integrated CCD aperture photometry | definitive | Revised New General Catalogue and Index Catalogue (RNGC/IC) |
| Distance in light-years | 49600000 ly | ± 3600000 ly | Multi-band Tully-Fisher & PHANGS-HST Tip of the Red Giant Branch (15.2 ± 1.1 Mpc) | definitive | SIMBAD Astronomical Database (CDS) |
| Apparent major axis | 5.4 arcmin | ± 0.3 arcmin | Optical isophotal dimensions (5.4′ × 4.7′) | definitive | Revised New General Catalogue and Index Catalogue (RNGC/IC) |
| Heliocentric recession velocity | 2407 km/s | ± 3 km/s | H I 21-cm synthesis velocity field (rapid infall into Virgo Cluster) | definitive | SIMBAD Astronomical Database (CDS) |
J2000 Equatorial Sky Chart & Culmination Altitude
The chart below plots Coma Pinwheel Galaxy (Messier 99 / NGC 4254) at RA 12h 18m 49.63s, Dec +14° 24′ 59.3″ within Coma Berenices, 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 15, 1781, Messier 99 (NGC 4254, the Coma Pinwheel or St. Catherine's Wheel) was the second galaxy after M51 in which Lord Rosse recognized a distinct spiral pattern in the spring of 1846. Situated 49.6 million light-years away on the western edge of the Virgo Cluster in Coma Berenices, M99 is an unbarred SA(s)c spiral measuring ~78,000 light-years across and plunging into the Virgo Cluster for the first time at a peculiar velocity exceeding 1,200 km/s.
Unlike symmetric two-armed spirals, M99 is famous for its lopsided, three-armed morphology: two tightly wound northern and eastern arms contrast with a single, wide-flung southwestern spiral arm pulled far away from the core. Radio 21-centimeter observations with the Arecibo and Very Large Array telescopes trace a colossal 800,000-light-year stream of neutral hydrogen gas (including the starless gas cloud VIRGOHI 21) trailing northward from M99—wrenched out of the galaxy by a high-speed gravitational flyby with Messier 98 (or dark-matter subhalos) roughly 750 million years ago.
Because M99 is still entering the Virgo Cluster and retains abundant molecular gas, its star-formation rate is three times higher than typical cluster spirals of its mass, fueling four recorded supernovae (SN 1967H, 1972Q, 1986I, and 2014L) and a 2023 luminous red nova transient.
Practical Visual Observing Guide
- Located 0.9° southeast of the 5th-magnitude star 6 Comae Berenices (which serves as the western signpost for both M98 and M99).
- At magnitude 9.9 and 5.4′ diameter, M99 has a relatively high surface brightness for a face-on spiral and is readily visible as a round, bright-centered glow in 80–100 mm telescopes.
- After M51, M33, and M101, M99 is one of the easiest spirals to resolve visually: in a 250–350 mm (10–14 inch) telescope at 140×–200× under dark skies, the prominent, detached southwestern spiral arm curves counterclockwise away from the core.
Catalog Cross-Identifications & Aliases
Common Aliases: M99 · NGC 4254 · UGC 7345 · St. Catherine's Wheel · Coma Pinwheel
| Catalog Authority | Identifier |
|---|---|
| MESSIER | M 99 |
| NGC | NGC 4254 |
| SIMBAD | M 99 |
| WIKIDATA | Q14070 |
Related Objects, Comparisons & Guides
Mirror Galaxy (Messier 100 / NGC 4321)
J2000 coordinates, HST Cepheid distance (53.8 Mly), magnitude 9.35, grand-design spiral arms, five supernovae, and observing guide for Messier 100.
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.
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.
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
- 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