Supernova SN1994D. Hubble Space Telescope (HST) image of supernova SN1994D (lower left) in the galaxy NGC 4526. A supernova is the explosive death of a star. Its outer layers are thrown into space in a huge explosion, which can rival the brightness of an entire galaxy, as seen here. This was a Type 1a supernova, all of which have the same brightness. This allows their distance to be calculated by how bright they appear from Earth. NGC 4526 has a small, bright nucleus (centre) and thick bands of dust in its arms. This galaxy is part of the Virgo cluster of galaxies lying some 55 million light years from Earth.