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ORIONID METEOR SHOWER: Next weekend, Earth will pass through a stream of debris from Halley's Comet, source of the annual Orionid meteor shower. Forecasters expect ~25 meteors per hour when the shower peaks on Oct. 21st. [video] [full story] [NASA Chat]
METEOR MAKES LANDFALL: A small asteroid that exploded over the San Francisco Bay Area on Oct. 17th, shaking houses with its sonic boom, might have scattered pieces of itself on the ground. That's the conclusion of Peter Jenniskens of the NASA Ames Research Center. He triangulated data from a pair of meteor surveillance cameras to determine the fireball's trajectory, denoted by the black arrow in the map below:
"The asteroid entered at a [relatively slow] speed of 14 km/s. There's a good chance that a fairly large fraction of this rock survived and fell somewhere around the North Bay," says Jenniskens. "Much more accurate results will follow from a comprehensive study of the video records. Now, we hope that someone recovers a meteorite on the ground."
In the map, red dots represent the surveillance cameras Jenniskens used to calculate the trajectory. The black arrow traces the asteroid's path; 85 km and 39 km are the altitudes of the asteroid at the two ends of the arrow. Jenniskens adds that "39 km is not the end point, but the final bit captured by the San Mateo video camera." The disintegrating asteroid continued beyond the tip of the arrow for a possible landfall somewhere north of San Francisco. Stay tuned for updates on the meteorite hunt.
GROUND AND SKY CURRENTS: For the second day in a row, a ~500 km/s solar wind speed is buffeting Earth's magnetic field, igniting auroras around the Arctic Circle. In Lofoten Norway on Oct. 17-18, the reverberating magnetic field induced electrical currents in the ground. "When we saw the currents on our monitors, we rushed outside to see the auroras," says Jan Koeman, who took this picture:
"It was a beautiful display," says Koeman. NOAA forecasters estimate a 10% to 15% chance of geomagnetic activity around the Arctic Circle tonight in response to the waning solar wind stream. However, based on Koeman's experience--"This was our sixth night in a row with clear skies and auroras," he says--the odds of a light show seem even higher. Arctic sky watchers should remain alert for auroras on Oct. 19th, especially during the hours around local midnight. Aurora alerts: text, voice.
Realtime Aurora Photo Gallery
SUN HALOS: As the northern hemisphere heads deeper into autumn, and ultimately winter, icy clouds become more commonplace. In other words, 'tis the season for sun halos. Charles Yeager photographed this specimen over Cleveland, Minnesota on Oct. 15th:
"This halo looked extremely large over the farm land of southern Minnesota," says Yeager.
In fact, it was 22 degrees in radius. That's how much hexagonal ice crystals in cirrus clouds bend the light of the sun overhead. Related crystals can also create sun pillars, sundogs, and a variety of other luminous halos. Look around the sun; you never know what you might see.
Realtime Space Weather Photo Gallery
Realtime Noctilucent Cloud Photo Gallery
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