Exploding comet visible to naked eye*

    * Story Highlights
    * Comet 17P/Holmes explodes, making its cloud bigger than Jupiter
    * Comet can be seen in the northern sky, in the constellation Perseus
    * Scientist: "This is a once-in-a-lifetime event to witness"

KNOXVILLE, Tennessee (AP) -- A comet that unexpectedly brightened in the
last couple of weeks and is now visible to the naked eye is attracting
professional and amateur interest.

Comet 17P/Holmes is seen among the stars of the constellation Perseus in
the North-Eastern sky.

Paul Lewis, director of astronomy outreach at the University of
Tennessee, is drawing students to the roof of the Nielsen Physics
Building for special viewings of Comet 17P/Holmes.

The comet is exploding and its coma, a cloud of gas and dust illuminated
by the sun, has grown to be bigger than the planet Jupiter. The comet
lacks the tail usually associated with such celestial bodies but can be
seen in the northern sky, in the constellation Perseus, as a fuzzy spot
of light about as bright as the stars in the Big Dipper.

"This is truly a celestial surprise," Lewis said. "Absolutely amazing."

Until October 23, the comet had been visible to modern astronomers only
with a telescope, but that night it suddenly erupted and expanded.

A similar burst in 1892 led to the comet's discovery by Edwin Holmes.

"This is a once-in-a-lifetime event to witness, along the lines of when
Comet Shoemaker-Levy 9 smashed into Jupiter back in 1994," Lewis said.

Scientists speculate the comet has exploded because there are sinkholes
in its nucleus, giving it a honeycomb-like structure. The collapse
exposed comet ice to the sun, which transformed the ice into gas.

"What comets do when they are near the sun is very unpredictable," Lewis
said. "We expect to see a coma cloud and a tail, but this is more like
an explosion, and we are seeing the bubble of gas and dust as it expands
away from the center of the blast."

Experts aren't sure how long the comet's show will last but estimate it
could be weeks if not months. Using a telescope or binoculars help bring
the comet's details into view, they said.