The Ikeya-Seki comet may have seemed a dud to casual observers who were screened from its spectacular passage by assorted weather conditions. It was by no means a disappointment to astronomers. Never before has a comet undergone such detailed scientific scrutiny—from observatories around the world, from specially outfitted jet planes, from NASA's sounding rockets.
Five times as luminous as a full moon, Ikeya-Seki lived up to its advance billing as one of the brightest comets of the century. Japanese astronomers boast that they snapped the clearest daylight pictures ever taken of a comet. Because of its...