Diagram showing the highly elliptical orbit of Halley's comet (red). The eight white circles represent the orbits of the planets Neptune (outermost),Uranus,Saturn,Jupiter,Mars,Earth,Venus & Mercury,with the Sun shown as the white dot at the centre. Halley's orbit takes it out beyond Neptune,but not as far out as the orbit of Pluto. Its orbit lies 18 degrees below the plane of the planetary orbits. Halley returns to the centre of the solar system on average every 76 years; it was last seen in 1910,prior to its return in 1985/86 |