Comet Hale-Bopp. Optical image of cometHale-Bopp seen over silhouetted trees. Both thegas and dust tails of the comet are seen. The gasor "ion" tail (blue) consists of ionized glowinggas blown away from the comet head by the solarwind. The dust tail (white) consists of grains ofdust pushed away from the comet head by theradiation of sunlight. A comet's tail alwayspoints away from the Sun. Comets have a nucleus ofice and dust. As they approach the Sun theirsurface evaporates, releasing a tail that can bemillions of kilometres long. Comet Hale-Bopp wasdiscovered on 23 June 1995. Photographed on 4April 1997 in Finland.. Stunning Photo Gifts From Science Photo Library