All the planets orbit the Sun in the same direction; looked at from a position above the Solar System, they move counter-clockwise. The speed at which each planet travels depends on its distance from the Sun, those closer moving faster than those farther out. Thus Mercury, the planet closest to the Sun, moves at a speed of 47.87 km/sec (29.75 mls/sec), whereas Pluto, the outermost of the planets, travels at only 4.74 km/sec (2.95mls/sec). So while Mercury takes only 88 Earth days to complete one orbit of the Sun, Pluto takes 248.5 Earth years - more than a thousand times longer.

Another feature common to all the planets is that they rotate about their axes as they orbit the Sun. One complete axial rotation is a day, but this period is highly variable. On Venus, for example, axial rotation takes approximately 243 Earth days, while on Jupiter a complete rotation takes a little less than ten hours. Also varying is the degree of axial inclination of the planets. For example, the Earth's polar axis is inclined at an angle of 23*27' to the vertical (the vertical being measured with respect to the plane of the Earth's orbit). For Venus, however, the axis is inclined at 178*C while the axial inclination of Jupiter is a mere 3*05'.

As well as these larger, named plantes, none of which has a diameter smaller than one-quarter of the Earth's, the Solar System contains a host of other bodies. Concentrated mainly between Mars and Jupiter, there are tens of thousands of asteroids that orbit the Sun, the largest of which is Ceres, with a diameter of 974 km (605mls).

Also in the Solar System are meteors and comets. Comets have elongated elliptical orbits which lie at quite wide angles to the plane of the Solar System. If the size of the Solar System is taken as being the distance these comets travel from the Sun before starting to return, then the solar System extends some two light-years out into space.