QUIET SUNSPOTS: The solar disk is peppered with large sunspots, yet none of them is actively flaring. Solar activity is low despite the high sunspot number.
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 (about one fourth the energy of the 'Little Boy' bomb dropped on Hiroshima), 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.
Solar wind
speed: 384.4 km/sec
density: 14.7 protons/cm3
explanation | more data
Updated: Today at 1656 UT
X-ray Solar Flares
6-hr max: C1 1213 UT Apr23
24-hr: C2 0201 UT Apr23
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Updated: Today at: 1600 UT
Daily Sun: 22 Apr 12
A new sunspot is groing at the circled location, further boosting the sunspot number. Credit: SDO/HMI
Sunspot number: 118
What is the sunspot number?
Updated 21 Apr 2012
Spotless Days
Current Stretch: 0 days
2012 total: 0 days (0%)
2011 total: 2 days (<1%)
2010 total: 51 days (14%)
2009 total: 260 days (71%)
Since 2004: 821 days
Typical Solar Min: 486 days
Updated 21 Apr 2012
The Radio Sun
10.7 cm flux: 149 sfu
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Updated 22 Apr 2012
Current Auroral Oval:
Switch to: Europe, USA, New Zealand, Antarctica
Credit: NOAA/POES
Planetary K-index
Now: Kp= 2 quiet
24-hr max: Kp= 4 unsettled
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Interplanetary Mag. Field
Btotal: 13.6 nT
Bz: 3.7 nT south
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Updated: Today at 1656 UT
Coronal Holes: 21 Apr 12
There are no large coronal holes on the Earthside of the sun. Credit: SDO/AIA
