Comet Hyakutake. Time-exposure view of Comet Hyakutake against star trails. Comet Hyakutake, or 1996 B2, was one of the brightest comets of the 20th century. Comets are mostly formed of water ice and dust. They usually have a diameter of a few kilometers and orbit the Sun with highly elongated orbits. It is only when a comet approaches the Sun that the water ice vaporizes to form a tail of gas and dust. This always points away from the Sun because it is blown away by the solar wind and radiation which the Sun emits. Star trails are formed by the motion of the stars across the sky during the photograph's exposure. This photograph was taken on 24th March 1996.