PHOENIX -- An urban comet that has burst into view and increased its brightness a million-fold in less than 24 hours, baffling astronomers and amateur stargazers.

Comet Holmes has looped around the Sun 16 times since it was first spotted in 1892. It is bright enough to be seen through city light pollution and moonlight.

PHOTOS: View Comet Up Close

Unlike most comets, it does not have a distinctive tail.

It shines with its yellowish core as the third brightest "star" in the Perseus constellation.

On Oct. 24, for no apparent reason, the comet, about 152,000,000 miles from Earth, erupted from a very dim magnitude 17 to about magnitude 2, astronomers said.

Astronomers are trying to unlock the mysteries of the celestial light show.

The Lowell Observatory in Flagstaff said such comet eruptions typically result from the sudden release of particles or outgassing.

Knoxnews.com said the mystery of the explosions could be linked to sinkholes within the nucleus of the comet, which is 2.11 miles in diameter. The sinkholes give the nucleus a porous structure, similar to a honeycomb.

If one of these chambers collapses, a large area of fresh cometary ice suddenly is exposed to the sun's heat and radiation. This causes the ice to rapidly transform from a solid directly to a gas, according to knoxnews.com.

Astronomers believe that comets are leftover debris from a collection of gas, ice, rocks, and dust that formed the outer planets about 4.6 billion years ago.

Where To Look

To see the comet, all you have to do is step outside and look to the Northeast.

MAP: Where To Look

You should be able to see the "W" that is the constellation Cassiopeia, it's standing on its end, according to NASA.

One and a half "fists" away to the right is a bright star in the constellation Perseus.

You probably won't be able to see all the Perseus stars, but the bright one, Mirfak, should be visible. It marks the top of a triangle, which is about the size of your thumb held at arms length away.

The triangle's lower left corner is the comet.

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