Comet ISON is approaching its encounter with the sun, forecast for Thursday, something astronomers await anxiously since this is an astronomical event rarely seen.

ISON will pass a relatively scant 1 million kilometers (620,000 miles) from the sun's surface, which has experts wondering if it will be destroyed by the solar turbulence or survive to star in an amazing celestial spectacle coinciding with Thanksgiving Day in the United States.

The comet will reach its perihelion, the moment when it will be closest to the sun, on Thursday.

"Remember: Comet ISON is a dynamically new sungrazing comet, fresh in from the Oort Cloud (at the edge of the solar system), and the last time we saw an object like this was never! When we factor in your standard 'comets are unpredictable' disclaimer, what we have is a huge recipe for the unknown," Karl Battams, an astrophysicist and computational scientist who has been posting regular updates on NASA's Comet ISON Observing Campaign Web site, said in a blog entry.

Scientists note that if ISON, dubbed the "Comet of the Century" does not disintegrate as it passes by the sun, which is at the peak of its cycle with numerous eruptions, it could radiate an astonishing light and remain visible throughout the month of December from Earth's Northern Hemisphere.

The comet, which has been traveling for at least a million years, increases its velocity the closer it gets to the sun, and on Thursday will be speeding through space at some 1.3 million kph (828,000 mph). EFE