ocr: COMET A celestial body orbiting around the Sun with an orbit quite eccentric. Typically, comets have diameters of a few kilometres, shapes not necessarily spherical, are not very dense, and are composed of ice and rocky material. When far from the Sun a comet is only a dark object in dark space. When it approaches the Sun's vicinity, it becomes visible. Evaporation of the nucleus' material generates the como, a gaseous envelope up to thousands of kilometres long. The coma and the nucleus together form the head of the comet. The tail forms later, when solar heating evaporates the head. The mate ...
