TIME BOMB?
Tick-tock, tick-tock. It's been 71 days since Comet 17P/Holmes exploded on Oct. 24, 2007, brightening almost a million-fold to naked-eye visibility. This means it could be time for another explosion. To understand why 71 days is significant, we turn back the clock to the year 1892.
Comet Holmes was discovered on Nov. 6, 1892, by astronomer Edwin Holmes while he was making observations of the Andromeda Galaxy. He noticed the comet not far from Andromeda when it "exploded"--a brightening akin to that of Oct. 2007. It was quite a sensation as observers around the world suddenly were able to see the comet with the naked eye. Interest faded as the comet expanded and dimmed, but then, 71 days later on Jan. 16, 1893, Holmes exploded again! Deja vu?
No one knows why Holmes occasionally explodes. Theories range from tiny moonlets crashing into the comet's icy surface to great comet-caverns collapsing under the stress of sunlight. The interval 71 days may have no significance at all. But on this anniversary of a double explosion, it reminds us to keep an eye on Comet 17P/Holmes.
Finding the comet is easy. Tonight, after sunset, take your binoculars outside and scan the northern constellation Perseus: sky map. Holmes is readily visible as a big pale fuzzball near the variable star Algol. On January 21-23, the comet will pass directly in front of Algol; the view through a backyard telescope should be dynamite!
http://www.spaceweather.com/