|
CAN PEOPLE GO TO
MARS? A new study shows that an 18-month
mission to Mars could expose astronauts to more space radiation
than NASA shielding technology can handle. Long-term missions to
the Moon could be problematic, too. Get the full
story from Science@NASA.
EIFFEL LIGHTNING
BOLT: Believe it or not, bolts of lightning
are shooting out of the Eiffel Tower. Photographer Hakim
Atek caught it happening on May 25th:
Photo Details: Nikon D80 + Nikkor
18-135mm, ISO 100, f/8, 30s, +2.0ev
"I saw some lightning out the window of my home in Paris,"
says Atek. "So I set up a tripod and pointed my camera (a Nikon
D80) at the Eiffel Tower. I never expected to get such an amazing
picture."
But did the Tower really make its own lightning? The surprising
answer is "yes."
"The upward branching in this photo shows that the Eiffel
Tower actually initiated the discharge," says lightning researcher
Richard Blakeslee of the NASA Marshall Space Flight Center. "In
other words, instead of starting in the cloud and coming to ground,
this flash started when the tower 'launched' a leader that propagated
upward toward the cloud (which still served as the source of the
electric field needed to get the process going). As the leader ascended,
it branched out. Eventually one of the branches reached a region
of sufficient charge to 'short out the cloud' and produce the return
stroke pictured above."
According to Martin Uman's classic text The Lightning Discharge,
upward-initiated discharges are "relatively rare," accounting
for less than 1% of all lightning, "and generally occur from
mountain tops and tall man-made structures." K. Berger, who
studied lightning from a mountaintop location 30+ years ago, was
one of the first to describe the phenomenon. Reference:
Blizstrom-parameter van aufwarsblizen, Bull. Schweiz. Elektrotech.,
69, 353-360, 1978.
more images: from
Jens Hackmann of Wuerzburg, Germany; from
David Hough of Warner's Bay, NSW, Australia; from
Joe Cascio of Buffalo, New York;
JUPITER'S MOON SHOW:
Every six years, Earth spends a number of
months passing through the orbital plane of Jupiter's moons. During
the passage, amateur astronomers get to see a rare display of "mutual
occultations." Jupiter's moons eclipse one another in plain
view of backyard telescopes.
On May 25th, Mike Salway of Central Coast, Australia, watched Ganymede
pass in front of Io. Click on the still-frame to launch a 0.25 MB
movie:
Images like these are unprecedented. Although Jupiter's moons put
on the same kind of show in 2002-2003, no one recorded such clear
pictures. "Imaging techniques and equipment have improved immensely
over the past 6 years," notes Salway. "So this is the
first year where amateurs are recording these events and producing
detailed, high-resolution images of the phenomena."
If you missed the Ganymede-Io eclipse, don't worry. There are plenty
more to come. Mutual occultations of Jupiter's moons will continue
from now until nearly the end of the year. As part of the International
Year of Astronomy, professional astronomers are organizing a worldwide
observing campaign to record as many of these events as possible.
Click here
for details.
more images: from
Efrain Morales Rivera of Aguadilla, Puerto Rico; from
Paul Maxson of Surprise, Arizona
April
2009 Aurora Gallery
[previous Aprils: 2008,
2007, 2006,
2005, 2004,
2003, 2002]
Explore
the Sunspot Cycle
|
