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SUN: With no sunspots actively
flaring, the sun's output has flatlined
again. NOAA forecasters put the chance of an
flare during the next 24 hours at no more than 1%.
Solar activity should remain low. Solar
flare alerts: text,
WHIRLPOOL: On Feb. 14-15, Arctic
skies erupted with an unexpected display of auroras
that veteran observers said was among the best in
months. At the height of the event, a US Defense
Meteorological Program satellite photographed a
whirlpool of Northern Lights over the Bering Sea:
of images from the DMSP F18 satellite captured
the dramatic auroral event of the last couple nights,"
says analyst Paul McCrone, who processed the data
at the US Navy's Fleet Numerical Meteorology and
Oceanography Center in Monterey, CA.
The reason for the outburst is still
not completely clear. It started on Feb. 14th when
rippled around the north pole. No CME was obvious
in local solar wind data at the time; the disturbance
just happened. Once begun, the display was amplified
by the actions of the interplanetary magnetic field
(IMF). The IMF near
Earth tipped south, opening a
crack in our planet's magnetic defenses. Solar
wind poured in and fueled the auroras.
more images: from
Göran Strand of Östersund, Sweden; from
Heidi Pinkerton of Birch Lake, Babbitt, Minnesota;
Roger Schneider of Tromso, Norway; from
Hanneke Luijting of Tromsø, Norway; from
Peter Rosén of Abisko NP, Sweden; from
Jesper Grønne of Silkeborg Denmark
DISAPPEARING TRICK: US spy satellite
Lacrosse 5 occasionally confounds observers by disapppearing:
In a matter of seconds, it can fade more than three
astronomical magnitudes. Is this a deliberate form
of stealth? Most experts think not, but no one outside
of classified circles knows for sure what is going
To investigate, French astrophotographer
Legault used his satellite-tracking telescope
to photograph Lacrosse 5 as it sailed 490 miles
above Paris on Jan. 15, 2012, and he caught the
the act of disappearing:
"During the passage, the brightness
of the satellite decreased by 10 times in only 4
seconds (a loss of 2.5 magnitudes)," describes
Legault. "After 33 seconds of [dark flight]
it regained its original brightness. Lacrosse 5
often shows this very singular behaviour, which
is called by other observers (especially Marco
Langbroek) the 'disappearing trick.'"
Other Lacrosse satellites do not perform
the same trick, at least not to this extent, suggesting
that the design of Lacrosse 5 differs from its predecessors.
The fade is likely caused by some sort of self-shadowing--e.g.,
maybe some part of the spacecraft such as its solar
panels casts a shadow over the main body when the
spysat changes attitude.
Even Legault's fine images do not
reveal the answer. "The cause of the disappearing
trick, as well as the precise shape of the satellite,
Readers, would you like to try catching
the tricks of Lacrosse 5? Check SpaceWeather's Simple
Satellite Tracker and Flybys
App for local flyby times.
2012 Aurora Gallery
[previous Januaries: 2010,
[previous comets: McNaught,