1994d

The bright spot in the lower left is SN 1994D, a star in the midst of a supernova, in the galaxy NGC 4526. During this final performance, the star will briefly outshine its parent galaxy. No supernovae have been observed in our galaxy in over four hundred years.

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NASA Astronomy Picture of the Day 2015 May 31

Supernova 1994D and the Unexpected Universe 

Long ago, far away, a star exploded. Supernova 1994D, visible as the bright spot on the lower left, occurred in the outskirts of disk galaxy NGC 4526. Supernova 1994D was not of interest for how different it was, but rather for how similar it was to other supernovae. In fact, the light emitted during the weeks after its explosion caused it to be given the familiar designation of a Type Ia supernova

If all Type 1a supernovae have the same intrinsic brightness, then the dimmer a supernova appears, the farther away it must be. By calibrating a precise brightness-distance relation, astronomers are able to estimate not only the expansion rate of the universe (parameterized by the Hubble Constant), but also the geometry of the universe we live in (parameterized by Omega and Lambda). The large number and great distances to supernovae measured over the past few years, when combined with other observations, are interpreted as indicating that we live in a previously unexpected universe.