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NGC 604
Emission nebula
H II region
	NGC 604 inside the Triangulum Galaxy; (viewed by the James Webb Space Telescope)
Observation data: J2000 epoch
Right ascension	01h 34m 33.2s
Declination	+30° 47′ 06″
Distance	2,700,000 ly (840,000 pc)
Apparent magnitude (V)	+14.0
Apparent dimensions (V)	1.93′ x 1.2′ arcmins
Constellation	Triangulum
Physical characteristics
Radius	760 ly
Absolute magnitude (V)	-13.8
Notable features	massive H II region; 3.5 million years old
	See also: Lists of nebulae

NGC 604 is an H II region inside the Triangulum Galaxy. It was discovered by William Herschel on September 11, 1784. It is among the largest H II regions in the Local Group of galaxies; at the galaxy's estimated distance of 2.7 million light-years, its longest diameter is roughly 1,520 light years (~460 parsecs), over 40 times the size of the visible portion of the Orion Nebula. It is over 6,300 times more luminous than the Orion Nebula, and if it were at the same distance it would outshine Venus. Its gas is ionized by a cluster of massive stars at its center^[4] with 200 stars of spectral type O and WR, a mass of 10⁵ solar masses, and an age of 3.5 million years;^[2] however, unlike the Large Magellanic Cloud's Tarantula Nebula central cluster (R136), NGC 604's one is much less compact and more similar to a large stellar association.^[5]

References

^ ^a ^b ^c ^d "NASA/IPAC Extragalactic Database". Results for NGC 604. Retrieved 2006-09-03.
^ ^a ^b ^c Barba, Rodolfo (2004). "An in-depth analysis of a prototypical giant H II region: NGC 604". HST Proposal ID #10419: 10419. Bibcode:2004hst..prop10419B.
^ distance × sin( diameter_angle / 2 ) = 760 ly. radius
^ Nemiroff, R.; Bonnell, J., eds. (2 November 2002). "NGC 604: Giant Stellar Nursery". Astronomy Picture of the Day. NASA.
^ Maíz-Apellániz, J.; Pérez, E.; Mas-Hesse, J. M. (2004). "NGC 604, the Scaled OB Association (SOBA) Prototype. I. Spatial Distribution of the Different Gas Phases and Attenuation by Dust". The Astronomical Journal. 128 (3): 1196–1218. arXiv:astro-ph/0406130. Bibcode:2004AJ....128.1196M. doi:10.1086/422925. S2CID 8099926.