Summary

Comets—some of the more spectacular celestial objects—have been observed and puzzled over for centuries. Despite what seems like a smoky tail, comets are cold, icebound space travelers with mostly elliptical (oval) orbits. Edmond Halley, a friend of Sir Isaac Newton and amateur astronomer, correctly predicted the reappearance of the comet that bears his name over a 300-year span using Newton's laws and accounting for the gravitational influence of Jupiter and Saturn. Comets carry gasses solidified into ice that return to their gaseous state as the comet draws closer to the heat of the sun. They originate in the far, frozen regions of the solar system and consist of the coma, or aura composed of ice and dust particles, the core or nucleus, and the tail. So-called meteor showers are caused by solid debris that breaks...