The Triangulum Galaxy, also catalogued as Messier 33 and NGC 598, is a sprawling face-on spiral that ranks among the most rewarding yet demanding targets for wide-field astrophotography. With an apparent magnitude of 5.72 mag spread across an angular size of 1.0° × 0.6° (60′ × 35′), its light is distributed over a large area, giving it a low surface brightness of around 22.67 mag/arcsec² that calls for dark skies and generous integration time. Short focal lengths frame the entire disk comfortably and reveal its loosely wound arms studded with pink HII regions, while H-alpha data dramatically enhances those star-forming knots. Patient exposure brings out the faint outer spiral structure and the galaxy’s characteristic blue-tinged arms against the dark backdrop of space.
Names, key data and data sources
All values come from the astronomical database SIMBAD (CDS Strasbourg). Tap a row to see where the value comes from.
NamesTriangulum GalaxyAstrocamp
Catalogue numbersM 33 (Messier 33) · NGC 598 · UGC 1117 · PGC 5818Primary designation: M 33SIMBAD
TypeGalaxyMorphology SA(s)cdSIMBAD
ConstellationTriangulum (Tri)computed
Position (J2000)RA 01h 33m 51s · Dec +30° 39′ 37″SIMBAD
Galactic coordinatesl = 133.6° · b = −31.3°Position relative to the Milky Way plane: 31° south of itcomputed
Brightness5.7 magBand V (visual) · B 6.3 magSIMBAD
Apparent size1.0° × 0.6° (60′ × 35′)SIMBAD
Orientation22°Position angle of the major axis, measured from north through eastSIMBAD
Distance2.8 million light-years850 kpcSIMBAD
Diameter48,000 light-yearscomputed
Blueshiftz = −0.00060−179 km/s: approaching usSIMBAD
Sources and methods (12)
- Names: Names from the Astrocamp object database.
- Catalogue numbers: All identifiers under which SIMBAD lists the object; order according to the Astrocamp catalogue rule.
- Type: Entry in SIMBAD, object type “GiG”. Morphology: quality D. Publication: 2013AJ....146...67B (NASA ADS). Value since Oct 20, 2026 · last confirmed with SIMBAD Oct 20, 2026
- Constellation: Computed from the position (IAU constellation boundaries). Value since Oct 20, 2026 · last confirmed with SIMBAD Oct 20, 2026
- Position (J2000): Entry in SIMBAD, accuracy ± 0.28 milliarcseconds, quality A (SIMBAD scale A–E). Publication: 2020yCat.1350....0G (NASA ADS). Value since Oct 20, 2026 · last confirmed with SIMBAD Oct 20, 2026
- Galactic coordinates: Converted from the position (IAU 1958 galactic system). Publication: 2020yCat.1350....0G (NASA ADS). Value since Oct 20, 2026 · last confirmed with SIMBAD Oct 20, 2026
- Brightness: One catalogue value, band V, error ± 0.0 mag, quality D (SIMBAD scale A–E). Publication: 2007ApJS..173..185G (NASA ADS). Value since Oct 20, 2026 · last confirmed with SIMBAD Oct 20, 2026
- Apparent size: One catalogue value, measured in visible light, quality D (SIMBAD scale A–E). Publication: 2003A&A...412...45P (NASA ADS). Value since Oct 20, 2026 · last confirmed with SIMBAD Oct 20, 2026
- Orientation: One catalogue value, measured in visible light, quality D (SIMBAD scale A–E). Publication: 2003A&A...412...45P (NASA ADS). Value since Oct 20, 2026 · last confirmed with SIMBAD Oct 20, 2026
- Distance: Median of all 16 measurements listed in SIMBAD (methods: Cep 5, T-F 3, redshift 2, kin 1, T-RGB 1, T-RDB 1), middle half 2.7 million light-years – 3.0 million light-years, full range 2.4 million light-years – 13 million light-years, 1 measurement(s) deviate by more than a factor of 1.5, rounded according to the scatter. Value since Oct 20, 2026 · last confirmed with SIMBAD Oct 20, 2026
- Diameter: Computed from the major axis and the distance; takes the weaker rating of the two values.
- Blueshift: One catalogue value, error ± 1.7 km/s, quality C (SIMBAD scale A–E). For such nearby galaxies it mainly reflects their own motion, not the expansion of the universe. Publication: 2012AJ....144....4M (NASA ADS). Value since Oct 20, 2026 · last confirmed with SIMBAD Oct 20, 2026
Checked against SIMBAD on Oct 20, 2026 · Open M 33 in SIMBAD
Position and the cosmic neighborhood
The Triangulum Galaxy sits in the small northern constellation Triangulum at right ascension 01h 33m 50.9s and declination +30° 39′ 37″, placing it high in the sky for observers at mid-northern latitudes during autumn evenings. It lies within the Local Group and is often considered a companion to the great Andromeda Galaxy, with the two separated by only a modest stretch of sky — a convenient pairing for astrophotographers planning a multi-target session. Its generous physical diameter of about 48,000 light-years and nearby location make it a bright anchor for wide-field compositions that can sweep across this corner of the Local Group.
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Nice to Know
- At around 2.8 million light-years away — a value derived as the median of 16 published measurements — it is one of the closest spiral galaxies to our own.
- Despite a bright overall magnitude of 5.72 mag, its light spreads over roughly a full degree of sky, so its low surface brightness makes it trickier to image well than its brightness suggests.
- It is the third-largest member of the Local Group, spanning about 48,000 light-years across, after the Andromeda Galaxy and the Milky Way.
- Its blueshifted radial velocity of -179.2 km/s shows the galaxy is approaching us rather than receding, a trait shared with the nearby Andromeda Galaxy.
