Transcript: A supernova is the violently explosive death of a star with the corresponding release of radiant energy, a flood of neutrinos, and the creation and ejection of heavy elements into space, the most spectacular phenomena in astronomy. Supernovae can occur in two basically different ways. In one way an isolated massive star has a core which is beyond the Chandrasekhar limit, and it collapses further to cause an explosion and leave a stellar remnant. A star with an initial mass of about six times the mass of the Sun will leave a core about 1.1 solar masses. A star about eight times the mass of the Sun will leave a core of 1.4 solar masses, the Chandrasekhar limit, and so stars more massive than eight times the mass of the Sun as they begin their lives will die as supernovae called Type I Supernovae. The second type of supernovae, Type II Supernovae, occur in binary systems where a more massive star is in orbit around a white dwarf just below the Chandrasekhar limit. As mass is transferred in the binary system from the more massive star onto the white dwarf, and as the white dwarf exceeds the Chandrasekhar limit, it explodes in a well regulated way. So the luminosity of Type II Supernovae is a well determined number.