To know the paths of the planets it is necessary to know only twelve constellations out of the seventy or more in the entire heavens; but it is difficult to imagine any one’s learning these twelve without becoming interested in and more or less acquainted with many of the splendid stars and constellations that lie on each side of them. The larger one’s acquaintance is with the appearance of the skies as a whole, the easier, naturally, it will be to distinguish the planets from the stars, and to follow their courses. But the planets themselves may be intimately known quite apart from any but the twelve constellations forming the zodiac. Happily, among them we shall find some of the most beautiful constellations in the heavens, and some of the most splendidly brilliant first-magnitude stars.[1] [1] The reader will find fuller descriptions of the stars in the zodiac in _The Friendly Stars_, by the author of this book. The twelve constellations of the zodiac are as follows: Pisces, the Fishes. Aries, the Ram. Taurus, the Bull. Gemini, the Twins. Cancer, the Crab. Leo, the Lion. Virgo, the Virgin. Libra, the Scales or Balance. Scorpio, the Scorpion. Sagittarius, the Archer. Capricornus, the Goat. Aquarius, the Water-Carrier. We shall begin at the point of the vernal equinox to trace the line of the ecliptic through these constellations, and that line will mark for us the path of the sun, the moon, and all the planets. It is convenient to begin at this point, because it is where the sun crosses the equator in the spring, and hence it is at the beginning of that part of the ecliptic which lies north of the equator. The point of the vernal equinox is now situated in the constellation Pisces. It is not marked by any bright star, but is not very difficult to find. It marks the point on the eastern horizon where the sun rises about March 21st, and about the 21st of September it is on the eastern horizon exactly opposite that point in the western sky where the sun sets. It is always ninety degrees from the pole, and if one chances to know the constellation Cassiopeia, which is shaped like a chair and is on the opposite side of the pole from the Big Dipper, one can locate the vernal equinox by drawing a line from the pole-star through the star which marks the lower part of the front of the chair, and extending it until it is ninety degrees long. The ninety degrees can be estimated by using the distance between the pointers in the Dipper (which is five degrees) as a measure. The star mentioned in Cassiopeia is about thirty-two degrees from the north star. [Illustration: MAP SHOWING THE CONSTELLATIONS OF THE ZODIAC AND THE LINE OF THE ECLIPTIC RUNNING THROUGH THEM The paths of all the planets, save one, lie always within three degrees of the ecliptic.]