Comet Hyakutake. Comet Hyakutake (at lower right), showing the comet's bright head (coma) and long tail. Comet Hyakutake or 1996 B2 was one of the brightest comets to appear in the sky this century. Comets are mostly formed of water ice and dust. They usually have a diameter of a few kilometres and orbit the Sun with highly elongated orbits. It is only when a comet approaches the Sun that the water ice vaporises to form a tail of gas and dust. This always points away from the Sun because it is blown by charged particles (the solar wind) which come out of the star. The image was taken on 13 March 1996; the brightest star (at upper centre) is Algol (Beta Persei).