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APOPHIS PRE-ANNIVERSARY:
Twenty years from today, on April 13th,
2029, asteroid
Apophis will buzz Earth only 18,300 miles above the planet's
surface--well inside the belt of geosynchronous communications satellites.
At closest approach, the 300-meter-wide asteroid will shine like
a 3rd magnitude star, visible to the unaided eye from cities in
Africa, Europe and Asia. There is a small
chance (1 in 45,000) that the 2029 encounter will bend the asteroid's
orbit so that it returns to Earth and actually hits the planet on
April 13th, 2036. Experts believe that future observations will
probably rule out a collision. Nevertheless, NASA and others are
thinking about asteroid
deflection strategies ... just in case.
RADIO STORMS ON JUPITER:
On April 11th, the loudspeaker of Thomas
Ashcraft's 21 MHz radio telescope in New Mexico suddenly began to
hiss and crackle. The sounds grew louder as Jupiter rose in the
blue morning sky. "I am pleased to report," says Ashcraft,
"a successful
recording
of Jovian S-bursts--the first of 2009." Click on the image
to listen:
The staccato pops sound like lightning in the loudspeaker of a
car radio, but lightning did not make these sounds. S-bursts
are caused by natural radio lasers in Jupiter's magnetosphere that
sweep past Earth as Jupiter rotates. Electrical currents flowing
between Jupiter's upper atmosphere and the volcanic moon Io can
boost these emissions to power levels easily
detected by ham radio antennas on Earth. Jovian S-bursts and
L-bursts can mimic the sounds of woodpeckers, whales, and waves
crashing on the beach. Here are a few audio samples:
S-bursts,
S-bursts
(slowed down 128:1), L-Bursts
"I recorded the storm in broad daylight," notes Ashcraft.
"One of the advantages of this long solar minimum is that the
daytime ionosphere is quieter and more transparent to decametric
radio waves. There will definitely be more
good Jupiter storms in the months to come." Stay tuned!
SUNDOGS AND DONKEY
SHADOWS: The next time you're out walking
on a sunny day and you meet a donkey, duck into its shadow. It's
a great place to find rings around the sun:
Yesterday, Erwan Henry of Carnac, France, followed
those instructions and found five different ice
haloes: "I saw a parhelic circle with sundogs, a 22o
sun halo, an upper tangent arc and an infralateral arc. I was so
happy to see an entire parhelic
circle for the first time!"
Halos like these are often overhead--and just as often
overlooked because there is nothing handy to block the glare. Can't
find a donkey? Fingers,
trees,
flags
and weather
globes work, too. Take a look!
Explore
the Sunspot Cycle
April
2009 Aurora Gallery
[previous Aprils: 2008,
2007, 2006,
2005, 2004,
2003, 2002]
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