Supernovas are divided into classes based upon the appearance of their spectra: hydrogen lines are prominent in Type II supernovas; hydrogen lines are absent in Type I supernovas.

This tells us that the progenitor stars either had hydrogen in their outer envelopes or did not have hydrogen in their outer envelopes. Type II supernovae are associated with the collapse and explosion of the cores of massive stars while Type Ia supernovae are associated with the explosion of massive white dwarfs in white dwarf binary star systems.

There is a less clean distinction between Type I and Type II supernovas in terms of their lightcurves. Although, we learn later that Type Ia SN show enough regularity in their lightcurves that they can be used as standardizable candles.

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