The word “comet” means “a hairy star.” But comets are not stars really, though they have often been mistaken for stars, especially when first seen without any tail. There may be any number of comets as far away as the stars, millions of them in each direction. But those we cannot possibly see. We only see such comets as belong to our Sun and travel about in his kingdom, or else those which come to pay him a visit from far away. No comet that is outside the Solar System can be visible to us on the Earth. The distance becomes too great. For the light of a comet is not like the light of a star, and it cannot reach through billions of miles, as the light of a star can. Once in a while a splendid comet makes its appearance, with a tail reaching half across our sky. But this is not at all common. Most of those seen are small and faint, and the greater number can only be seen at all in telescopes. Almost every year some fresh ones are found in the sky, and hardly a day passes in which at least one may not be noticed, in some part of the heavens, with a good telescope. Each comet, like each world, has its own pathway in the sky round the Sun. But a comet-pathway is much more oval in shape than a planet-pathway. Sometimes it is a very long and very narrow oval indeed, with the Sun almost close to one end of the long oval. To get round such a pathway as this takes a good while. At one part the comet gets quite near to the Sun, and then rushes at a tremendous speed. After which he wanders far away from the Sun, and creeps along more and more slowly. There are comets belonging to the Solar System which draw closer to the Sun than Mercury and go farther away than Neptune. Comet-pathways do not keep to the level of the chief planet-pathways. They slope about in all manner of ways, like the paths of the little Planetoids. Very many comets belong to the Sun’s kingdom. They journey round and round the Sun, and appear again and again from time to time. Some take only a few years for their journey, while others come back only once in the life of a man; and others again may be hundreds of years absent. And some comets never return. They do not belong to our Sun, but only pay him a single visit. These are strangers to our kingdom of worlds, travelling from the kingdom of some other far-off sun, perhaps one of the twinkling stars in our sky. A stranger comet comes, like other comets, slowly from the distance, quickening his speed day by day as he gets nearer to the Sun. Then he rushes at a mad rate round the Sun and flies off in a new direction, to quite another part of the heavens. What wonderful stories these bright visitors might tell us, if they could speak, of the skies from which they arrive! A comet is made of three parts: the _nucleus_, or the thickest portion of the head; the _coma_, or the bright fog round the nucleus; and the _train_ or _tail_.