The Solar System

The solar system consists of the Sun; the nine planets Mercury, Venus, Earth, Mars, Jupiter, Saturn, Uranus, Neptune and Pluto; sixty one (61) satellites of the planets, a large number of small bodies (the comets and asteroids), and the interplanetary medium.

The orbits of the planets are ellipses with the Sun at one focus. The orbits of all except Mercury and Pluto are very nearly circular. The orbits of the planets are all more or less in the same plane (called the ecliptic and defined by the plane of the Earth's orbit). The ecliptic is inclined only 7 degrees from the plane of the Sun's equator. Pluto's orbit deviates the most from the plane of the ecliptic with an inclination of only 17 degrees. They all orbit in the same direction (counter-clockwise looking down from above the Sun's north pole); all but Venus and Uranus also rotate in that same sense.