Comet Ikeya-Zhang, optical image. This bright comet was visible in the northern hemisphere in spring 2002. The Andromeda Galaxy (M31, NGC 224) is seen below the comet's head. Ikeya-Zhang has two distinct tails. The ion tail (blue) comprises glowing ionised gas blown away from the comet's head by the solar wind. The dust tail (white/pink) comprises grains of dust pushed away from the head by the radiation of sunlight. This tail shines by reflected sunlight only. Both tails always point away from the Sun, regardless of the comet's direction of travel. Ikeya-Zhang is thought to orbit the Sun with a period of around 367 years. Photographed from Finland on 4th April 2002.