Comet Hale-Bopp, 1997. Image of the comet Hale-Bopp (C/1995 O1, lower centre) as it passed near the Earth. Hale-Bopp was one of the brightest and most widely observed comets of the 20th Century. It was visible to the naked eye for a record 18 month, twice as long as the previous record holder, the Great Comet of 1811. The comet has two clear tails; a white dust tail and a blue ion tail. The dust tail is formed of dust particles blown off the comet by sunlight. The ion tail is made up of glowing ionised gas pushed off the comet by the charged solar wind. Both tails always point away from the Sun. Photographed in 1997.