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CHANCE
OF FLARES: Sunspot AR1465 has developed
a 'beta-gamma-delta' magnetic field that harbors
energy for X-class
solar flares. Because of the sunspot's location
near the middle of the solar disk, any eruptions
will likely be Earth-directed. Solar
flare alerts: text,
phone.
QUIETING
STORM, MORE TO COME: Earth's magnetic
field is quieting after two straight nights of mild
to moderate geomagnetic storms. At the height of
the disturbance on April 23-24, auroras were spotted
in more than a dozen US states including Michigan,
Nebraska,
Kansas,
Wisconsin,
North
Dakota, South
Dakota, Iowa,
Illinois,
Minnesota,
and Colorado.
On the threshold of the Arctic Circle in Anchorage,
Alaska, the Northern Lights pierced the glow of
the midnight sun:
"I didn't think I would get another
glimpse of the auroras this season because of the
increasing daylight," says photographer Ryan
Delos Reyes, "but this was a spectacular show."
More auroras may be in the offing.
A minor CME is en route to Earth, due to arrive
on April 26th. NOAA forecasters estimate a 20% to
30% chance of geomagnetic storms. 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.
