SN1993J lights northern sky.

Nothing brightens the night sky - or an astronomer's workday - like a super-nova, the death of a massive star. On March 28, amateur astronomer Francisco Garda Diez of Lugo, Spain, discovered a supernova, designated SN 1993J, in the galaxy M81. After confirming the finding, astronomers turned a battery of orbiting and ground-based instruments toward SN1993J(arrow), which lies about 12 million light-years from Earth in the constellation Ursa Major.

Though not visible without a telescope, SN1993J is the brightest super-nova to appear above the northern hemisphere in decades. A review of previously obtained images of M81 shows that SN1993Jwas once a red supergiant. After exhausting its nuclear fuel, the star collapsed and exploded. Now, as the ensuing shock wave moves outward, it plows through gas cast off by the star in past centuries. This gas crackles with energetic X-rays bearing information about SN1993J's chemical composition and evolution.

Garcia discovered the supernova around the same time that astronomers activated Japan's new Advanced Satellite for Cosmology and Astrophysics (ASCA). "It's astonishing that we've been this lucky," says George R. Ricker of the Massachusetts Institute of Technology, who helped design one of ASCA's X-ray detectors. Using ASCA and other satellites, astronomers will monitor changes in SN1993J's emissions and perhaps detect the ultradense neutron star that may lie hidden at its center.