This shell expands the outer atmosphere of the star to over 10 up to 1000 solar radii. The entire life of the star from main sequence to supergiant is only a few million years. I suggest that white dwarfs stars within a binary system may blow off accumulated material as a supernova. Type II spectra reveal hydrogen lines, while Type I do not. Finally, Type I light curves peak then smoothly taper, while a type II light curve resembles a bumped and bruised Type I light curve.
Astronomers use supernova data to estimate a distance to the supernova.
Most observed supernova lie within other galaxies, thus astronomers can check distance calibrations and the expansion rate of the universe, or Hubble Constant . In addition, supernova observations show the relative element amounts blown into the interstellar medium. The remainder of the stellar atmosphere that the supernova blows away into interstellar space. Astronomers see spectral emission of elements processed in the late stages of stellar evolution, like nitrogen, oxygen, and neon. The material is still hot and rushes through space at hundreds of kilometers per second.