Comet Hale-Bopp (C/1995 O1)

One of the brighter comets of the twentieth century, notable for its very large size. Discovered by Alan Hale and Thomas Bopp on 22 July 1995, it reached perihelion on 1 April 1997 and achieved a maximum brightness of around magnitude -1. Its core was estimated to be 40 km (25 miles) across, over twice the diameter of Halley's Comet.