William Herschel discovered NGC 604 = H III-150 = h133 on 11 Sep 1784 (sweep 266) and noted "vF, S, R nebula, brightest in the middle." Lord Rosse or assistant reported on 13 Sep 1850: "large spiral full of knots, north following is a bright, small neb [NGC 604], which on a very good night might appear attached to the spiral, than which it is brighter." Bindon or George Stoney measured an offset from a star superimposed just north of the core of M33 on 2 Jan 1851 and the nebula was labeled as "3" on the diagram in the 1861 publication.

200/250mm - 8" fairly bright, round, knot in M33.

300/350mm - 13.1" (7/5/86): bright HII region located 12' NE of the core of M33. Situated at the end of the large spiral arm of M33 that extends north and then east of the core. Bright, fairly small, ~30" diameter, round.

400/500mm - 18" (12/10/07): bright, large HII knot in M33 at the end of the spiral arm that trails to the east on the north side of the core. A mag 10.5-11 star is located 1.5' SE and NGC 604 is elongated 3:2 in the direction of this star. The outline is oval, though a bit irregular, particularly on the east side. It appears brighter and mottled on the northwest side and with direct vision a slightly brighter stellaring is embedded near the northwest end.

Notes by Steve Gottlieb