In this program, scientists around the world follow a once-in-a-lifetime event, the path of the sun-grazing comet ISON. The comet, somewhere between one and 10 kilometers in diameter, is currently just beyond the orbit of Jupiter. As it races past Earth toward the sun, it will likely develop a tail to light up the night skies. Then ISON will slingshot around the back of the sun, to emerge perhaps brighter than ever. But there's jeopardy, too; ISON could evaporate completely, or the sun's gravity could tear it apart, producing a so-called "string of pearls" - several small comets arching across the night sky.