Comet Hale-Bopp. Optical image of comet Hale-Bopp. Hale-Bopp was one of the brightest comets of the 20th century. Its gas or 'ion' tail (blue) consists of ionized glowing gas blown away from the comet head by the solar wind. The dust tail (white) consists of grains of dust pushed away from the comet head by the radiation of sunlight. Comets have a nucleus of ice and dust. As they approach the Sun their surface evaporates, releasing a tail millions of kilometers long. Photographed on 1st April 1997.