Comet HaleBopp. Optical image of comet HaleBopp showing its gas and dust tails, seen over trees. HaleBopp 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 kilometres long. Comet HaleBopp was discovered on 23 June 1995. Photographed on 6 April 1997 near Wesel, Germany.