Type Ia supernovae follow a characteristic light curve—the graph of luminosity as a function of time—after the event. This luminosity is generated by the radioactive decay of nickel-56 through cobalt-56 to iron-56. The peak luminosity of the light curve is extremely consistent across normal type Ia supernovae, having a maximum absolute magnitude of about −19.3. This is because type Ia supernovae arise from a consistent type of progenitor star by gradual mass acquisition, and explode when they acquire a consistent typical mass, giving rise to very similar supernova conditions and behavior. This allows them to be used as a secondary standard candle to measure the distance to their host galaxies.