Number 69 (Story #1), February 27, 1992 by Phillip F. Schewe and Ben Stein SUPERNOVA 1987A IS FIVE YEARS OLD . The brightest supernova in four centuries, SN1987A is now dimmer than its progenitor star, Sanduleak -69 202, but it still entertains astronomers. The lightcurve, long dominated by radiation from the decay of radioactive cobalt-56, may now be more dependent on radiation from the longer-lived isotope cobalt-57. Meanwhile a ring of gas surrounding SN1987A (at a radius of 0.68 light years) was illuminated (beginning in 1988) by light from the supernova. Measurements by the Hubble Space Telescope of the ring's angular diameter allowed the most accurate estimation yet of the distance between SN1987A and the Earth. Some scientists expect that the ring will brighten further when, around the turn of the century, the supernova shockwave itself reaches the gas ring. (Astronomy, Feb. 1992; Nature 20 Feb. 1992; New Scientist, 22 Feb. 1992.)