Halley's Comet begins its 38-year journey back toward Earth tonight

Beginning on Friday, Dec. 8 we can finally state with absolute certainty that Halley's Comet is coming.This most famous of all comets travels around the sun in a flattened elliptical orbit that brings it near to the sun and then takes it far out to beyond the outer limits of the solar system. Ever since Feb. 9, 1986, when it arrived at perihelion — the comet's closest approach to the sun — it then began its long journey back out into distant space. And from that time up until the present, the comet has been moving inexorably away from the sun.But at 8 p.m. Eastern Time on Friday, Dec. 8, (0100 GMT on Dec. 9.) that will come to an end. For at that moment, Halley's Comet will arrive at aphelion; the far end of its orbit — that location in space that places the comet at its farthest point from the sun: 3.27 billion miles (5.26 billion km) distant. The comet will be then be 472.2 million miles (759.8 million km) beyond the orbit of Neptune, the most distant known planet.The last time Halle...