Astronomy Picture of the Day

Explanation: In 1994, a new star in a distant galaxy was seen by amateur astronomers, who alerted the world to their discovery of a supernova. Near the nucleus of spiral galaxy M51, popularly known as the Whirlpool, this supernova (1994I) is identified as the bright spot indicated by the arrow in the lower left of this Hubble Space Telescope image. Supernovae are violent death explosions of stars that eject radioactive debri clouds. They are often discovered by amateur observers dedicated to systematic searches of the sky and are of intense interest to astronomers who hope to learn what kind of stars generate these explosions and what chemical elements are produced and mixed into space. Distances to these these intrinsically bright events can also be determined, providing crucial yardsticks for measuring the Scale of the Universe.