|
COMET LULIN UPDATE:
"Right now, Comet Lulin (C/2007 N3)
is an easy target for binoculars and small telescopes," reports
Mariano Ribas of Buenos Aires, Argentina. "It is visible despite
our strong urban light pollution. I have been observing the comet
during the hours before dawn and estimate its visual magnitude as
+7. Maybe this will not be a 'great' comet like McNaught was two
years ago, but I look forward to a good show in the weeks ahead
as Comet Lulin approaches Earth." [gallery]
[sky map]
[finder chart]
HUBBLE FLARE:
The Hubble Space Telescope is not the brightest light in the night
sky. Soaring overhead, it typically shines like a 2nd magnitude
star, a pinprick of middling luminosity and nothing to get excited
about--that is, not until it flares. "Last night, I saw the
Hubble brighten dramatically," reports Mark
Staples of Waldo, Florida. "It was almost as bright as
Venus." He captured the flare during an 82-second exposure
with his Canon
30D:
Hubble flares have been observed before. They are caused by sunlight
glinting off the flat back surface of the spacecraft where the primary
mirror is located.
The sudden glints are practically impossible to predict. They depend
not only on the ever-changing shape of the Sun-Earth-Hubble triangle,
but also on the details of Hubble's observing schedule. The pointing
of the telescope determines how the back-plane is tilted and, thus,
the possibility of a flare. The only way to catch one is to spend
time looking.
Check the Simple Satellite Tracker to find
out when Hubble is going to fly over your backyard. You may be in
for a pleasant surprise!
LEE WAVE IRIDESCENCE:
Invisible to the human eye, air flowing
over the Rocky Mountains bobs up and down in giant waves known as
lee waves.
On Jan. 2nd, these waves became temporarily visible when clouds
caught in the wave-pattern lit up with beautiful iridescence:
"The pastel colors were lovely and the billowing cloud shapes
were quite fascinating," says photographer Harold
Leinbach of Boulder, Colorado. "I took the picture using
my Canon
Rebel XT."
Iridescence is caused by droplets of water diffracting sunlight.
We often see hints of iridescent color in ordinary clouds far from
mountain ranges. Lee waves intensify the phenomenon, creating a
sky-wide tableau of vivid pastel.
Atmospheric optics expert Les Cowley explains: "For brightly-colored
iridescence you need cloud droplets of all the same size. You get
that if all the droplets have formed at the same time and experienced
the same history. Dynamic conditions inside a lee cloud are just
what the doctor ordered. The clouds look stationary but inside there
is a 'factory
conveyor' with uniform droplets formed at one end and evaporated
at the other. Voila - iridescence."
Lee waves may be found downwind of all mountains--not just the
Rockies. If you live in the lee, keep an eye out for pastels in
the sky.
|
