By Henry K. Lee

The fireball that lit up the predawn Northern California sky last week was a small comet that flamed out when it hit the Earth's atmosphere, a researcher said.

The comet "instantly turned into dust and gas," resulting in the flash of light seen by many at 5:21 a.m. last Thursday, said meteor hunter Peter Jenniskens, a scientist at the Seti Institute in Mountain View.

Because the comet vaporized, no pieces fell to Earth, Jenniskens said.

The comet came into contact with the Earth's atmosphere just north of Yosemite National Park at a speed of 160,000 mph, Jenniskens said.

"Moving toward Lake Tahoe, the small comet then penetrated to lower elevations where it fully disrupted in the atmosphere," Jenniskens wrote Tuesday on his group's website.

The sight was a treat for those up and about before dawn. One witness said it resembled "a giant orange crayon."

Reports of the sighting came in from around California and from outside Reno.

It was the second cosmic sighting in the Bay Area in three months. On Oct. 17, a monster fireball lit up the skies, and several chunks of it - meteorites - were later found in the Novato area.

Henry K. Lee is a San Francisco Chronicle staff writer. E-mail: hlee@sfchronicle.com Twitter: @henryklee

Source: http://www.sfgate.com/science/article/Predawn-spectacle-was-flaming-comet-4215218.php