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SUNSET
PLANETS: The brightest planets
in the night sky are aligning for a must-see show
in late February and March 2012. You can start looking
tonight. [video]
[full
story] [New images: #1,
#2,
#3,
#4,
#5,
#6,
#7,
#8]
SOLAR
ECLIPSE: Today, the new Moon passed
in front of the sun, off-center, producing a partial
solar eclipse. The only place to see it was from
space. NASA's Solar Dynamics Observatory (SDO) sends
this picture from geosynchronous orbit approximately
36,000 km above Earth's surface:
Using a bank of 16 megapixel cameras,
SDO observed the event at multiple extreme ultraviolet
wavelengths. Scan the edge of the Moon in this
171 Å image: The little bumps and irregularities
you see are lunar mountains backlit by solar plasma.
Beyond the novelty of observing an
eclipse from space, these images have practical
value to the SDO science team. The sharp edge of
the lunar limb helps researchers measure the in-orbit
characteristics of the telescope--e.g., how light
diffracts around the telescope's optics and filter
support grids. Once these are calibrated, it is
possible to correct SDO data for instrumental effects
and sharpen the images even more than before.
Update: A movie of
today's eclipse is now
available thanks to Steele Hill, SDO Media Specialist
at the Goddard Space Flight Center,
The next solar eclipse
visible from Earth's surface occurs on May 20, 2012:
video.
AURORAS
OVER THE USA: A solar wind stream
hit Earth's magnetic field during the late hours
of Saturday, Feb. 18th, sparking a G1-class geomagnetic
storm. Usually, auroras produced by such a mild
storm would be confined to Arctic latitudes. Not
this time. Northern Lights spilled across the Canadian
border into US states such as Wisconsin, Michigan,
Iowa, North Dakota, Nebraska and Minnesota. Bob
Conzemius video-recorded the display from the Chippewa
National Forest north of Grand Rapids, MN:
"It was fun watching the auroras
illuminate the fog and snow on the lake while listening
to barred owls calling," says Conzemius. "I
may have heard a couple wolves howling in the distance,
too."
In Nebraska "I saw auroras
on and off for approximately 2 hours from around
9pm to 11pm local time," reports Chris Allington
of Crofton, NE. "There was a brief spell where
color was visible to the eye with rays and bands."
Allington stitched together a series of 20s exposures
to create this
movie.
At the height of the display, researchers
at the Poker Flats Research Range outside of Fairbanks,
Alaska, launched a suborbital rocket to investigate
how auroras affect GPS systems. Several photographers
in the area caught the
rocket flying
into
the Northern Lights.
The surprising display might have
been amplified by the action of a co-rotating interaction
region or "CIR." CIRs are transition zones
between fast and slow solar wind streams. Solar
wind plasma piles up in these regions, producing
density gradients and shock waves that do a good
job of sparking auroras. Local solar wind data suggest
that Earth moved through a CIR around 1500 UT on
Feb. 18th. Aurora
alerts: text,
voice.
February
2012 Aurora Gallery
[previous Februaries: 2011,
2010,
2009,
2008,
2007, 2006,
2004, 2003,
2002]
SPY-SAT
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
on.
To investigate, French astrophotographer
Thierry
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
spysat in
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,
remain unknown."
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.
Comet
Lovejoy Gallery
[previous comets: McNaught,
Holmes,
Lulin,
Tuttle,
Ikeya-Zhang]
