Many of the emission sources are associated with H II regions of star formation. The four brightest HII regions are designated NGC 588, NGC 592, NGC 595, and NGC 604. These regions are associated with molecular clouds containing solar masses. The brightest of these regions, NGC 604, may have undergone a discrete outburst of star formation about three million years ago. This nebula is the second most luminous HII region within the Local Group of galaxies, at times the luminosity of the Sun. Other prominent HII regions in Triangulum include IC 132, IC 133, and IK 53.