#OTD in 1995.
Hale–Bopp, one of the most widely observed comets of the 20th century, was independently discovered by astronomers Alan Hale and Thomas Bopp, before it became visible to the naked eye.
It was visible to the naked eye for a record 18 months, due to its massive nucleus size. This is twice as long as the Great Comet of 1811, the previous record holder. Accordingly, Hale–Bopp was dubbed the great comet of 1997.