Number 124 (Story #1), April 16, 1993 by Phillip F. Schewe and Ben Stein SUPERNOVA 1993J , first spotted on March 28, is the brightest supernova in the northern hemisphere in several decades and the brightest supernova of any kind since SN 1987A. Alert astronomers and a fleet of versatile satellites contributed to what is the most thorough observation (at diverse wavelengths) of a supernova in its earliest stages. At the American Physical Society meeting in April in Washington, DC this week, Stephen Holt of NASA/Goddard---representing the Japanese satellite ASCA---and Walter Lewin of MIT---representing the German satellite Rosat---reported the detection of prompt x rays from SN 1993J. The distance of the supernova, 12 million light years away in galaxy M81, and the early arrival and intensity of the x rays (at the highest x-ray energies, the supernova was brighter than the galactic core) allowed scientists to estimate a supernova temperature of 100 million K and to deduce that the progenitor star had been a red supergiant star. According to this hypothesis, prompt x rays would arise from the supernova shock wave plowing into the high-density, low-velocity stellar wind (given off in the centuries before the blast) surrounding the star. By contrast, in the case of supernova 1987A, whose progenitor was a blue supergiant, the shock had to catch up to a low-density, high-velocity stellar wind, thus delaying the arrival of x rays for several months. George Sonneborn of NASA/Goddard reported on ultraviolet measurements of SN 1993J with the IUE satellite. From these he expects to learn about the red giant's stellar wind and the way in which it approached its violent death. Other telescopes such as the Hubble Space Telescope and the Gamma Ray Observatory will be looking at SN 1993J. However, because the new supernova is some 70 times further from Earth than SN 1987A, detected emissions will be about 5000 times weaker, virtually eliminating the probability of seeing neutrinos.