Comet Hale-Bopp (C/1995 O1) was the brightest comet seen in recent years, even though it came no closer to Earth than 1.32 AU (197,000,000 kilometers). Discovered independently by Alan Hale, director of the Southwest Institute for Space Research (New Mexico), and amateur astronomer Thomas Bopp (Arizona) on 22 July 1995, it reached perihelion on 1 April 1997, and was visible to the naked-eye for many months. Its nucleus seems to be very large – about 40 kilometers across – and spins around once every 11.4 hours. Last seen in 1997, Hale-Bopp has an orbital period of 2,380 years and won't be seen again until AD 4377.