Approaching comet may outshine the moon

* Comet ISON discovered in September

* Could be brightest comet in decades

Dec 28 (Reuters) - A comet blazing toward Earth could

outshine the full moon when it passes by at the end of next year

- if it survives its close encounter with the sun.

The recently discovered object, known as comet ISON, is due

to fly within 1.2 million miles (1.9 million km) from the center

of the sun on Nov. 28, 2013 said astronomer Donald Yeomans, head

of NASA's Near Earth Object Program at the Jet Propulsion

Laboratory in Pasadena, Calif.

As the comet approaches, heat from the sun will vaporize

ices in its body, creating what could be a spectacular tail that

is visible in Earth's night sky without telescopes or even

binoculars from about October 2013 through January 2014.

If the comet survives, that is.

Comet ISON could break apart as it nears the sun, or it

could fail to produce a tail of ice particles visible from

Earth.

Celestial visitors like Comet ISON hail from the Oort Cloud,

a cluster of frozen rocks and ices that circle the sun about

50,000 times farther away than Earth's orbit. Every so often,

one will be gravitationally bumped out from the cloud and begin

a long solo orbit around the sun.

On Sept. 21, two amateur astronomers from Russia spotted

what appeared to be a comet in images taken by a 16-inch

(0.4-meter) telescope that is part of the worldwide

International Scientific Optical Network, or ISON, from which

the object draws its name.

"The object was slow and had a unique movement. But we could

not be certain that it was a comet because the scale of our

images are quite small and the object was very compact,"

astronomer Artyom Novichonok, one of the discoverers, wrote in a

comets email list hosted by Yahoo.

Novichonok and co-discoverer Vitali Nevski followed up the

next night with a bigger telescope at the Maidanak Observatory

in Uzbekistan. Other astronomers did likewise, confirming the

object, located beyond Jupiter's orbit in the constellation

Cancer, was indeed a comet.

"It's really rare, exciting," Novichonok wrote.

Comet ISON's path is very similar to a comet that passed by

Earth in 1680, one which was so bright its tail reportedly could

be seen in daylight.

The projected orbit of comet ISON is so similar to the 1680

comet that some scientists are wondering if they are fragments

from a common parent body.

"Comet ISONcould be the brightest comet seen in many

generations - brighter even than the full moon," wrote British

astronomer David Whitehouse in The Independent.

In 2013, Earth has two shots at a comet show. Comet

Pan-STARRS is due to pass by the planet in March, eight months

before ISON's arrival.

NASA's Mars Curiosity rover may be able to provide a

preview.

Comet ISON is due to pass by the red planet in September and

could be a target for the rover from its vantage point inside

Gale Crater.

The last comet to dazzle Earth's night-time skies was Comet

Hale-Bopp, which visited in 1997. Comet 17P/Holmes made a brief

appearance in 2007.

(Editing by Kevin Gray and Leslie Gevirtz)

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