NASA Takes Footage of Comet ISON Approaching Sun

Astronomers still unsure what will happen next

Comet ISON, a shopping-mall-sized chunk of dust and ice that makes its closest approach to the sun Thursday, is refusing to show its hand. Researchers know it will skim roughly 1 million miles from the fiery solar surface around 1:30 p.m. ET, but what will happen next is the subject of feverish scientific speculation.

If the comet is still intact for its close encounter, there's a good chance it will become visible to the naked eye, perhaps as a glowing arc across the pre-dawn sky. On the other hand, if ISON disintegrates before its embrace with the sun, most of us on Earth will see … nothing.