The Triangulum Galaxy, also cataloged as Messier 33 and NGC 598, is a sprawling face-on spiral galaxy that ranks among the most rewarding yet demanding targets for wide-field astrophotographers. Its large angular size of 1.0° × 0.6° (60′ × 35′) means it easily fills the frame of short focal length refractors, but its low surface brightness of 22.6735 mag/arcsec² spreads its light thinly and calls for long total integration times to reveal the delicate spiral arms. Rich in glowing pink emission nebulae, this galaxy responds beautifully to hydrogen-alpha data that can be blended into broadband images to accentuate its star-forming regions. Dark skies and patient stacking are the keys to pulling out the faint outer arms and subtle structure that make Messier 33 a showcase object.
Names and Catalog numbers
- Triangulum Galaxy
- M 33 (Messier 33)
- NGC 598
- UGC 1117
- PGC 5818
Position and the cosmic neighborhood
Positioned at right ascension 01h 33m 50.9s and declination +30° 39′ 37″, the Triangulum Galaxy sits within the compact constellation Triangulum, tucked between the more prominent star patterns of Andromeda and Aries. Shining at an apparent magnitude of 5.72, it is a member of our Local Group and a close companion to the great Andromeda Galaxy, making it easy to frame alongside other galactic neighbors in the autumn sky. Its northern declination keeps it well placed for observers across the Northern Hemisphere, where it rides high overhead and offers dark, unobstructed skies for deep imaging sessions.
Nice to Know
- At roughly 13.4 million light-years distant, the Triangulum Galaxy is one of the nearest large galaxies to our own and a cornerstone member of the Local Group.
- Its true physical diameter spans about 235,000 light-years, giving it a generous footprint on the sky of 1.0° × 0.6° (60′ × 35′).
- The galaxy is approaching us with a radial velocity of -179.2 km/s, reflected in its slightly blueshifted redshift value of z = -0.000597568.
- Known by many designations including Messier 33, NGC 598, PGC 5818 and UGC 1117, it is celebrated for its abundant emission nebulae that make it a favorite for narrowband astrophotography.
Brightness, distance and size
The object has an apparent magnitude of 5.7 mag, it lies about 13.4 million light-years from Earth and spans roughly 235,000 light-years across. On the sky it appears about 1.0° × 0.6° (60′ × 35′) in size.
