It's crunch time for a comet from the fringes of the solar system as it hurtles toward a close encounter with the sizzling sun.
Comet ISON is expected to get closest to the sun at 1837 GMT (1:37 p.m. EST) on Thursday.
At that point it will be only about 1 million miles (1.6 million kilometers) away from the sun's surface.
Scientists say it probably won't be visible from Earth except via fleet of NASA telescopes and spacecraft. But if ISON survives—and it will be a few hours before that's known—and returns past Earth, astronomers say it should be easily visible in the Northern Hemisphere early next month, just before sunrise and after sunset.
Explore further: Video gives astronaut's-eye view inside NASA's Orion spacecraft