Comet Hale–Bopp was perhaps the most widely observed comet of the 20th century and one of the brightest seen for many decades. It was visible to the naked eye for a record 18 months, twice as long as the previous record holder, the Great Comet of 1811.
Hale–Bopp was discovered on 23 July 1995, at a great distance from the Sun, raising expectations that the comet would brighten considerably by the time it passed close to Earth. Although predicting the brightness of comets with any degree of accuracy is very difficult, Hale–Bopp met or exceeded most predictions when it passed perihelion on 1 April 1997. The comet was dubbed the Great Comet of 1997.