Short answers, pulled from the story.
A supernova is a powerful and luminous explosion of a star that occurs during the last evolutionary stages of a massive star or when a white dwarf triggers runaway nuclear fusion. Astronomers distinguish this phenomenon from ordinary novae by adding the prefix super- to the word nova because ordinary novae are far less luminous and do not destroy the underlying star.
Chinese astronomers documented SN 185 in AD 185 within the constellation of Centaurus and recorded the brightest supernova SN 1006 which appeared in AD 1006 in the constellation of Lupus with a maximum apparent magnitude of negative 7.5. Observers in China, Japan, Iraq, Egypt, and Europe described these events while Johannes Kepler began observing SN 1604 at its peak on the 17th of October 1604.
Theoretical studies indicate that most supernovae are triggered by either the sudden re-ignition of nuclear fusion in a white dwarf through material accumulation or stellar merger or the core collapse of a massive star once it begins fusing iron. This process expels several solar masses of material at speeds up to several percent of the speed of light into the surrounding interstellar medium.
Astronomers classify supernovae according to their light curves and the absorption lines of different chemical elements that appear in their spectra where Type II contains hydrogen lines and Type I lacks them. Specific subtypes include Type Ia which shows strong ionized silicon absorption near peak light and Type Ib which displays non-ionized helium lines.
Type Ia supernovae are produced from white dwarf stars in binary star systems while Wolf-Rayet stars act as the progenitors of Type Ib and Type Ic supernovae after losing most of their outer hydrogen envelopes. Red supergiants form the progenitors for the vast majority of core collapse supernovae but have been observed only at relatively low masses below about 15 solar masses.