PLAN'ET, noun [Latin planeta; Gr. wandering, to wander, allied to Latin planus. See Plant.] A celestial body which revolves about the sun or other center, or a body revolving about another planet as its center. The planets which revolve about the sun as their center, are called primary planets; those which revolve about other planets as their center, and with them revolve about the sun, are called secondary planets, satellites or moons. The primary planets are named Mercury, Venus, Earth, Mars, Jupiter, Saturn and Herschell. Four smaller planets, denominated by some, asteroids, namely, Ceres, Pallas, Juno and Vesta, have recently been discovered between the orbits of Mars and Jupiter. Mars, Jupiter, Saturn and Herschell, being without the earth's orbit, are sometimes called the superior planets; Venus and Mercury, being within the earth's orbit, are called inferior planets. The planets are opake bodies which receive their light from the sun. They are so named from their motion or revolution, in distinction from the fixed stars, and are distinguished from the latter by their not twinkling.