Figure 17.10: Supernova 1994D in the outskirts of the galaxy NGC 4526. This example of a type Ia supernova shows that at peak brightness they rival the cores of galaxies in luminosity. That is why they can be detected to great distances. At approximately 20 Mpc away, this galaxy is 'nearby' on the distance scales of the universe. How long ago did the supernova go off?