Why does Comet Halley come back regularly?
The comets we see follow a variety of paths across the expanse of our solar system. Some make a single pass into the region of the Sun and then retum to the deep freeze of the outer solar system, never to be seen again. Others may have long elliptical paths that will bring them back to us, but only after many thousands or millions of years have passed. Some comets, on the other hand, have had their orbits altered by the gravitational pull of the giant outer planets — Jupiter, Saturn, Uranus, and Neptune. These “short-period comets” — of which about 100 are known — mostly stay within the region of the planets and can thus grace our skies much more regularly. Comet Halley is a fine example of a short-period comet, taking about 76 years to make one orbit around the Sun. At its closest point (perihelion), the comet is only 88 million kilometers from the Sun (about 60% of the Earth’s distance from our star.) At its most distant point (aphelion), Halley is 5.2 billion kilometers from the Su
