Supernova 1994D in Galaxy NGC 4526

This image obtained by the Hubble Space Telescope shows the galaxy NGC 4526 and its supernova 1994D (lower left). Discovered with ground-based telescopes in March 1994, the supernova was, for a short time, brighter than all the rest of the stars in its host galaxy combined.

Supernova 1994D was a special kind of supernova, known as a Type Ia, that astronomers use to measure astronomical distances. Type Ia supernovas peak with roughly the same intrinsic brightness (meaning they all produce about the same amount of light). This allows astronomers to determine how far away each Type Ia supernova is by measuring how bright it appears. (Type Ia supernovas that appear fainter are farther, while those that appear brighter are closer.)

Measurements of Type Ia supernovas in distant galaxies like this one have helped astronomers refine their measurements of both the expansion rate and age of the universe.

Credit: NASA, ESA, the Hubble Key Project Team, and the High-Z Supernova Search Team