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GEOMAGNETIC STORM: A minor (Kp=5) geomagnetic storm is underway. This is probably due to Earth's passage through the wake of a CME that swept past our planet earlier today. Aurora alerts: text, phone.
SIERRA FIREBALL DECODED: On Sunday morning, April 22nd, just as the Lyrid meteor shower was dying down, a spectacular fireball exploded over California's Sierra Nevada mountain range. The loud explosion rattled homes from central California to Reno, Nevada, and beyond. According to Bill Cooke, head of NASA's Meteoroid Envronment Office, the source of the blast was a meteoroid about the size of a minivan.
"Elizabeth Silber at Western University has searched for infrasound signals from the explosion," says Cooke. "Infrasound is very low frequency sound which can travel great distances. There were strong signals at 2 stations, enabling a triangulation of the energy source at 37.6N, 120.5W. This is marked by a yellow flag in the map below."
"The energy is estimated at a whopping 3.8 kilotons of TNT, so this was a big event," he continues. "I am not saying there was a 3.8 kiloton explosion on the ground in California. I am saying that the meteor possessed this amount of energy before it broke apart in the atmosphere. [The map] shows the location of the atmospheric breakup, not impact with the ground."
"The fact that sonic booms were heard indicates that this meteor penetrated very low in atmosphere, which implies a speed less than 15 km/s (33,500 mph). Assuming this value for the speed, I get a mass for the meteor of around 70 metric tons. Hazarding a further guess at the density of 3 grams per cubic centimeter (solid rock), I calculate a size of about 3-4 meters, or about the size of a minivan."
"This meteor was probably not a Lyrid; without a trajectory, I cannot rule out a Lyrid origin, but I think it likely that it was a background or sporadic meteor."
News and eyewitness reports: #1, #2, #3, #4.
CRESCENT MOON ALERT: When the sun goes down tonight, step outside and look west into the twilight. You might see something like this:
Miguel Claro photographed the crescent moon from Almada, Portugal. "Look just below the bridge," he points out. "You can also see Jupiter."
The slender crescent will be beaming through the twilight for the next few evenings. On Tuesday, April 24th, it will glide by Venus for a spectacular sunset conjunction. Don't miss it!
more images: from Stefano De Rosa of Turin, Italy; from Robert Arn of Fort Collins, CO; from Russell Vallelunga of Phoenix, Arizona; from M. Raşid Tuğral of Ankara, Turkiye; from Zain Ahmed of Karachi, Pakistan
METEOR SHOWER RECAP: According to the International Meteor Organization, the Lyrid meteor shower peaked on April 22nd around 0000 UT with a maximum between 20 and 30 meteors per hour. This doesn't place the Lyrids among the year's best showers, but many observers were pleasantly surprised. "This year's Lyrid shower was much better than I expected! I saw dozens of meteors, mostly Lyrids, nice and quick ones," reports Monika Landy-Gyebnar, who caught this Lyrid over the glow of her hometown Veszprem, Hungary:
The meteors were serenaded by nightingales. "The birds arrived here about a week ago and they were constantly singing, which made the observation even more memorable!" she adds. "Imagine being out at night, surrounded by nightingales, with a bright Milky Way and meteors falling through our atmosphere - a wonderful celebration of Earth Day in 2012 which coincided with the Lyrid maximum!"
more images: from Pete Lawrence of Selsey, West Sussex, UK; from Shawn Malone near Marquette, Michigan; from Jimmy Westlake of Stagecoach, Colorado; from Darren Baskill of East Sussex, UK; from Brian Emfinger of Ozark, Arkansas; from Ivan Majchrovic of Marianka, Slovakia; from Peter Meadows of Chelmsford, Essex, UK; from Ireneusz Nowak of Wroclaw, Poland; from Michael Noble of Alberta, Canada;