Comet discovered in 1994 by the amateur astronomers Alan Hale and Thomas Bopp at a distance from the Sun of about seven astronomical unit s, beyond Jupiter 's orbit and farther than any comet detected before by amateurs.
Astronomers estimated its nucleus to be about 25 mi (40 km) in diameter, larger than most comets. At its closest approach to the Sun in April 1997, it was one of the intrinsically brightest comets in several centuries, though not the brightest as seen from Earth. The comet triggered the mass suicide near San Diego, Calif., U.S., in 1997 of 39 members of a religious cult known as Heaven's Gate , whose leader maintained that they would be reincarnated in a spacecraft following in the comet's wake.