This five-minute exposure taken at NASA's Marshall Space Flight Center in Alabama on November 8 shows the comet ISON when it was 97 million miles from Earth and heading toward a close encounter with the sun. (Aaron Kingery/NASA via Reuters)

A comet is heading for a close encounter with the sun later this month, and if it is not vaporized or torn apart, it should be visible to the naked eye in December.

Comet ISON is expected to pass about 621,000 miles from the sun on November 28.

Scientists are not sure how ISON will hold up. As it blasts around the sun, traveling at 234 miles per second, the comet will be heated to about 5,000 degrees, hot enough to vaporize not just ice in the comet’s body but also rock and metal.

If the heat does not kill ISON, the sun’s gravity may rip it apart. But recent calculations predict that ISON will survive.

The comet was discovered in September 2012 by two amateur astronomers using International Scientific Optical Network, or ISON, for which the comet is named.

It was extraordinarily bright at the time, considering its great distance beyond Jupiter’s orbit, raising the possibility of a truly cosmic spectacle as it approached the sun. That is because heat from the sun causes ice in a comet’s body to vaporize, creating bright, distinctive tails and fuzzy-looking, glowing bodies. Sometimes, the closer it comes to the sun, the brighter it shines.

Over the past 10 days, amateur astronomers began posting on the Web the first pictures of the comet to be taken with just binoculars or small telescopes.

“I finally saw Comet ISON for the first time using small binoculars!” pilot Brian Whittaker wrote on “It was faint, but is predicted to brighten and move each day! Exciting!”

Comets are believed to be frozen remains left over from the formation of the solar system about 4.5 billion years ago.

ISON’s group of comets is located in the Oort Cloud, a reservoir of icy bodies beyond Neptune’s orbit. Occasionally, an object is gravitationally bumped out of the cloud and into the inner solar system. Computer models show ISON is a first-time visitor.

The comet is moving through the constellation Virgo low in the eastern sky in the hours before dawn, astronomer Tony Phillips wrote on “It is still too dim for naked-eye viewing, but an increasingly easy target for backyard optics,” Phillips said.

If predictions prove correct, the comet should be visible to the naked eye in Earth’s early-morning skies in early December and throughout the night beginning in January.

— Reuters