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AURORA FORECAST: A solar wind stream is heading for Earth and it could spark a geomagnetic storm when it arrives on Oct. 28th. Sky watchers around the Arctic Circle should be alert for auroras.
FLASHBACK: One year ago today, on Oct. 24, 2007, Comet 17P/Holmes shocked astronomers when it suddenly exploded, brightening a million-fold to naked-eye visibility. Within three days of the blast, the comet was bigger than Jupiter, and within three weeks it was larger than the sun itself. Spanish photographers Vicent Peris and José Luis Lamadrid recorded this view on Nov. 1, 2007, using little more than a 7-inch telescope:
What happened to Comet Holmes? Just-released observations by NASA's Spitzer Space Telescope define the mass and velocity of the explosion: "The energy of the blast was about 1014 joules and the total mass was of order 1010 kg," says Bill Reach of Caltech. In other words, Holmes exploded like 24 kilotons of TNT and ejected 10 million metric tons of dust and gas into space. These numbers fit a model favored by Reach in which a cavern of ice some hundred meters beneath the comet's crust changed phase, from amorphous to crystalline, releasing in transition enough heat to cause Holmes to blow its top.
Holmes has exploded twice in recorded history--in 1892 and 2007. Two caverns down, how many to go? No one knows. Browse the gallery for a preview of what the next blast might look like:
Comet Holmes Photo Gallery
[JPL press release] [Night Sky Cameras]
ASTEROID FLYBY: "At midnight on Oct. 23rd, I began my lonely vigil," says Dennis Simmons of Brisbane, Australia. "I was hunting for 2008 TT26, a 70-meter asteroid scheduled to pass less than a million miles from our home planet Earth. What I hadn't anticipated was the frantic pace set by the little space rock as it zoomed through my field of view!" He captured this movie using a 9-inch Celestron telescope and an SBIG ST7e CCD camera:
Click on the image for photo details
Although on the scale of asteroids 2008 TT26 is small, it is still a dangerous object, about twice as wide as the mystery-rock that caused the Tunguska event of 1908. Fortunately, 2008 TT26 was beyond the orbit of the Moon when it made its closest approach on Oct. 23rd.
"Later that morning," says Simmons, "having seen the animation, my wife humoured my efforts, thanking me for keeping watch on the fast approaching lump of rock while she had slept soundly, glad that somewhat was looking out for planet Earth!"
more images: from Leonid Elenin of Mayhill, New Mexico
2008 Orionid Meteor Gallery
[IMO meteor counts] [2006 Orionids]