Triangulum Galaxy (Messier 33)
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.
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) | 5.72 mag | ± 0.1 mag | Wide-field integrated aperture photometry | definitive | Revised New General Catalogue and Index Catalogue (RNGC/IC) |
| Extragalactic distance | 859000 pc | ± 24000 pc | Cepheids + TRGB + VLBA water-maser geometric proper motion (2.80 ± 0.08 Mly) | definitive | SH0ES Local Distance Ladder Hubble Constant |
| Apparent major axis | 71 arcmin | ± 3 arcmin | Optical disk isophotal dimensions (71′ × 42′) | definitive | Revised New General Catalogue and Index Catalogue (RNGC/IC) |
| Mean visual surface brightness | 23 mag/arcsec² | ± 0.2 mag/arcsec² | Derived from V=5.72 spread over 71′ × 42′ face-on disk | definitive | Revised New General Catalogue and Index Catalogue (RNGC/IC) |
J2000 Equatorial Sky Chart & Culmination Altitude
The chart below plots Triangulum Galaxy (Messier 33 / NGC 598) at RA 01h 33m 50.89s, Dec +30° 39′ 35.8″ within Triangulum, 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 Triangulum Galaxy (Messier 33, NGC 598) is the third-largest member of the Local Group after Andromeda (M31) and the Milky Way, located 859 ± 24 kiloparsecs (2.80 million light-years) away in Triangulum—just 15° southeast of M31 on the sky and physically only ~750,000 light-years from Andromeda. Spanning ~61,000 light-years across and containing roughly 40 billion stars, M33 is a pure late-type SA(s)cd spiral galaxy lacking both a central bar and a supermassive central bulge.
Because we view M33 at a modest 54° inclination, its open, flocculent spiral arms reveal spectacular star-forming complexes across another galaxy. Chief among these is NGC 604 in M33's northeastern arm: a monstrous H II emission nebula spanning 1,500 light-years across (nearly 40 times the linear diameter of the Orion Nebula) and ionized by more than 200 young O-type and Wolf-Rayet stars.
In 2005 astronomers used Very Long Baseline Array (VLBA) radio interferometry to track the proper motions and Doppler velocities of water-vapor masers orbiting M33's center, measuring M33's rotation and geometric distance directly without relying on standard candles.
Practical Visual Observing Guide
- Under pristine Bortle 1–2 mountain or desert skies, experienced observers use M33 (magnitude 5.72) as the ultimate test of dark-adapted naked-eye vision at 2.8 million light-years.
- Under suburban skies (Bortle 5+), beginners often sweep right over M33 with high-power telescopes because its 23.0 mag/arcsec² glow fills the entire eyepiece; use 10×50 or 15×70 binoculars or a wide-field telescope at 20×–35× first!
- Once you locate the soft oval glow of M33, increase power to 100×–150× on the northeastern spiral arm to spot the extragalactic H II region NGC 604, which shines at magnitude 12.0 like a fuzzy planetary nebula inside another galaxy.
Catalog Cross-Identifications & Aliases
Common Aliases: M33 · NGC 598 · Pinwheel Galaxy in Triangulum
| Catalog Authority | Identifier |
|---|---|
| MESSIER | M 33 |
| NGC | NGC 598 |
| SIMBAD | M 33 |
| WIKIDATA | Q13738 |
Related Objects, Comparisons & Guides
Andromeda Galaxy (Messier 31 / NGC 224)
Coordinates, Cepheid/TRGB distance (765 kpc / 2.50 Mly), magnitude 3.44, blueshift (−300 km/s), and observing guide for Andromeda (M31).
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.
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.
Andromeda (M31) vs Triangulum (M33) Comparison
Compare the Local Group spirals Andromeda (M31) and Triangulum (M33): mass, inclination, surface brightness, and why M33 is a classic dark-sky test.
Surface Brightness vs Magnitude Field Guide
Field guide to how surface brightness (mag/arcsec²) and integrated magnitude govern naked-eye, binocular, and telescope visibility of nebulae and galaxies.
Autumn Sky Tour: Andromeda, Perseus & Cassiopeia
Autumn observing guide from Cassiopeia and Perseus (Double Cluster, Algol, Cas A) across Andromeda and Triangulum to Local Group galaxies M31 and M33.
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.
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.
NGC & Caldwell Deep-Sky Cross-Walk Catalog
Cross-reference guide to Dreyer's New General Catalogue (NGC) showpieces, including southern gems Omega Centauri, 47 Tucanae, Carina Nebula, and the Veil.
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