By DAVID PERLMAN
San Francisco Chronicle
November 13, 2007
It's an obscure and very faint comet that suddenly blazed into astonishing brilliance and is growing larger but dimmer -- and while it's still clearly visible all night long, astronomers are puzzling over the unexpected outburst.
"It's really bizarre," said Joseph Miller, a University of California Santa Cruz astronomer and former director of the Lick Observatory atop Mount Hamilton near San Jose. "That thing started out only a few miles in diameter, and suddenly it expanded at a thousand miles an hour until it was as big as the Earth within only a couple of days."
With a decent pair of binoculars -- or even with unaided eyes -- anyone can see the comet right now as a tiny, fuzzy, white object in the northern sky -- wherever fog doesn't obscure the sight. It lies just inside the constellation Perseus, below the more familiar constellation Cassiopeia and due east of Polaris, the North Star.
It's called Comet 17P/Holmes and was discovered in 1892 by the British astronomer Edwin Holmes, who spotted it as it appeared to explode in what Holmes thought was an outburst of gas. It faded, then exploded once more and finally appeared to die into permanent dimness.
Ever since then, Comet Holmes has been laying low -- so faint that no one paid any attention to it while larger, far brighter comets like Halley, Hyakutake, Kohoutek and Hale-Bopp put on their shows in recent years to the delight of stargazers everywhere.
Now amateur astronomers throughout the Bay Area have been having a fine time with Holmes, which began putting on its latest show two weeks ago.
"I've seen a lot of comets, but this one isn't like any comet I've ever seen," said Michael Portuesi, a San Francisco software engineer. "I watched it double in size within a couple of nights and it got really bright, very round and looked like a very pregnant star.
"Now it's more like a small, round puffball."
"It's certainly not your typical comet," said Jeff Rabb, an Oakland air travel broker. "It's a big fuzzy ball of light, and because it's right next to a star in Perseus, I thought at first it was some kind of strange comet with a double nucleus."
Terry Swanets, who lives among the redwoods around Guerneville, said he had a hard time spotting the comet because the trees kept swaying and blocking his view. It was also too foggy much of the time, but he gets a good look now and then and is impressed. "I never saw anything like it in my life," he said. "Amazing!"
Kenneth Frank, president of the San Francisco Amateur Astronomers, described the comet's recent sudden burst. "It just started brightening unexpectedly and it was incredible" he said. "And now that it's somewhat dimmer, I'd say it looks like the top of a dirty Q-tip. But you can still see it, even without binoculars."
According to astronomers at the Harvard-Smithsonian Observatory in Cambridge, Mass., Comet Holmes was obscure until Oct. 27 when it began flaring brilliantly, and within three days was nearly a million times brighter than it had been. Three days later, astronomer Pierre Bastien at the University of Montreal in Canada reported that Holmes was showing evidence of a faint cometary tail, but if the tail is there it's too faint for ordinary eyes to see.
"It's all still all a bit of a mystery, and people will be speculating about what's happening for a long time," said Miller at UC Santa Cruz. "There may have been some kind of trapped gas in the comet that unexpectedly vented as a result of heating from the sun, or the gas may have burst out from the impact of some unknown object colliding with it, although the comet is now flying fairly near Jupiter where objects like asteroids are extremely rare."
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