Short answers, pulled from the story.
The supernova SN 1006 appeared in the year 1006 and was visible in the constellation Lupus. It was witnessed by astronomers in China, Japan, Iraq, Egypt, and Europe, marking one of the most significant astronomical observations in human history.
The name supernova was coined in 1931 by Walter Baade and Fritz Zwicky. They needed a term to distinguish these powerful events from ordinary novae and to reflect the Latin word for new.
The two primary mechanisms are the sudden re-ignition of nuclear fusion in a white dwarf and the gravitational collapse of a massive star's core. The first process creates a Type Ia supernova while the second results in a core collapse supernova.
The brightest recorded event was SN 1006 which appeared in the year 1006 and was visible to the naked eye for months. It shone so brightly it cast shadows on the ground and rivaled the brightness of the entire Milky Way galaxy.
Astronomers classify supernovae based on their light curves and the absorption lines of different chemical elements that appear in their spectra. Type I supernovae lack hydrogen lines while Type II supernovae show hydrogen lines indicating the presence of a hydrogen envelope.
The red supergiant problem highlights the discrepancy between the number of red supergiants observed and the number of supernovae that should result from them. Many red supergiants appear to collapse directly into black holes without producing a visible supernova.