Bodies resembling the earth and of different sizes, which revolve in elliptical orbits round the sun, and at different distances, the chief of them eight in number, two of them, viz., Mercury and Venus, revolving in orbits interior to that of the earth, and five of them, viz., Mars, Jupiter, Saturn, Uranus, and Neptune, exterior , the whole with the planetoids ( q. v .) and comets constituting the solar system.