A nova (pl. )'s a cataclysmic nuclear explosion caused by the accretion of hydrogen onto the surface of a white dwarf star. Novae aren't to be confused with Type Ia supernovae, or another form of stellar explosion first announced by Caltech in May 2007, Luminous Red Novae. Occurrence rate, and astrophysical significance Astronomers estimate that the Milky Way experiences roughly 30 to 60 novae per year, with a likely rate of about 40. The number of novae discovered in the Milky Way each year's… (More on Nova)