I try to balance
the content aggregation I collect with the original material. Before another
movie review or trip report, let’s look at last week’s Astronomy Pictures of
the Day. In this week the moon was in focus with two different pictures, and
the week ended with some information about solar wavelengths to commemorate the
winter solstice.
Sunday, December 15
Explanation: Although the phase of this moon might
appear familiar, the moon itself might not. In fact, this gibbous phase shows part of Jupiter's moon Europa.
The robot spacecraft Galileo
captured this
image mosaic during its mission orbiting Jupiter from 1995 - 2003. Visible
are plains of bright ice, cracks that run to the
horizon, and dark patches
that likely contain both ice and dirt. Raised terrain is
particularly apparent near the terminator,
where it casts shadows. Europa is nearly the same
size as Earth's Moon, but
much smoother, showing few highlands
or large impact craters.
Evidence and images from the Galileo
spacecraft, indicated that liquid oceans might exist below the icy
surface. To test speculation that these seas hold life, ESA has started
preliminary development of the Jupiter Icy Moons
Explorer (JUICE), a spacecraft
proposed for launch around 2022 that would further explore Jupiter and in
particular Europa. Recent
observations by the Hubble Space
Telescope have uncovered new
evidence that Europa, like Saturn's moon Enceladus, has ice
venting from its surface.
Monday, December 16
Explanation: A new
desk-sized rover has begun exploring the Moon. Launched two weeks ago by the Chinese
National Space Administration, the Chang'e 3 spacecraft landed
on the Moon yesterday and deployed
the robotic rover. Yutu, named for a folklore lunar Jade Rabbit, has a
scheduled three-month mission to explore several kilometers inside the Sinus Iridum (Latin for
"Bay of Rainbows") impact crater. Yutu's cameras and spectrometers
will investigate surface features and composition while ground penetrating radar
will investigate deep soil structure. Chang'e 3
achieved the first soft Moon landing since the Soviet Union's Luna 24 in 1976, and Yutu is
the first lunar rover deployed since the USSR's Lunokhod 2 in 1973. Pictured
above, Yutu was imaged
from its lander
yesterday soon after rolling onto the Moon.
Tuesday, December 17
Geminid Meteors over Teide
Volcano
Image Credit & Copyright: Juan Carlos Casado (TWAN, Earth and Stars)
Image Credit & Copyright: Juan Carlos Casado (TWAN, Earth and Stars)
Explanation: On some nights
it rains meteors. Peaking two nights ago, asteroid dust streaked through the
dark skies of Earth, showering down during the annual Geminids
meteor shower. Astrophotographer Juan
Carlos Casado captured the space weather event, as pictured above, in a
series of exposures spanning about 2.3 hours using a wide angle lens. The
snowcapped Teide volcano of
the Canary Islands of
Spain towers in the
foreground, while the picturesque
constellation of Orion highlights the
background. The star appearing just near the top of the volcano is Rigel. Although the asteroid dust particles
are traveling parallel to each other, the resulting meteor streaks appear to radiate
from a single point on the sky, in this case in the constellation of Gemini, off
the top of the image. Like train
tracks appearing to converge in the distance, the meteor radiant
effect is due to perspective. The astrophotographer has estimated that there
are about 50 Geminids visible in the above composite image -- how many do you
see?
Wednesday, December 18
Light Pillars over Finland
Image Credit & Copyright: Thomas Kast
Image Credit & Copyright: Thomas Kast
Explanation: What's
happening behind those houses? Pictured above are not aurora but nearby light pillars, a local
phenomenon that can appear as a distant one. In most places on Earth, a lucky
viewer can see a Sun-pillar,
a column of light appearing to extend up from the Sun caused by flat fluttering ice-crystals reflecting
sunlight from the upper atmosphere. Usually these ice crystals evaporate before
reaching the ground. During freezing temperatures, however, flat
fluttering ice crystals may form near the ground in a form of light snow,
sometimes known as a crystal fog. These ice crystals may then reflect ground
lights in columns not unlike a Sun-pillar.
While going out to buy cat food, a
quick thinking photographer captured the above
light pillars extending up from bright parking lot lights in Oulu, Finland.
Thursday, December 19
Explanation: The Moon is normally seen in subtle
shades of grey or yellow. But small,
measurable color differences have been greatly exaggerated to make this
telescopic, multicolored, moonscape captured during the Moon's full phase. The
different colors are recognized to correspond to real differences in the chemical
makeup of the lunar surface. Blue hues reveal titanium rich areas
while orange and purple colors show regions relatively poor in titanium and
iron. The familiar Sea of
Tranquility, or Mare Tranquillitatis, is the blue area in the upper right
corner of the frame. White lines radiate across the orange-hued southern lunar
highlands from 85 kilometer wide ray crater Tycho at bottom left.
Above it, darker rays from crater Copernicus extend into the
Sea of Rains (Mare Imbrium)
at the upper left. Calibrated by rock samples from the Apollo
missions, similar multicolor images
from spacecraft have been used to explore the Moon's global
surface composition.
Friday, December 20
Explanation: Saturn's
large moon Titan would be unique in our solar system, the only world with stable
liquid lakes and seas on its surface ... except for planet Earth of course.
Centered on the north pole, this colorized map
shows Titan's bodies of methane and ethane in blue and black, still liquid at frigid surface
temperatures of -180 degrees C (-292 degrees F). The map is based on data from
the Cassini spacecraft's radar, taken during flybys between 2004 and
2013. Roughly heart-shaped, the lake above and right of the pole is Ligeia
Mare, the second largest known body of liquid on Titan and larger than Lake Superior on Earth.
Just below the north pole is Punga Mare. The sprawling sea below and right of
Punga is the (hopefully sleeping) Kraken
Mare, Titan's largest known
sea. Above and left of the pole, the moon's surface is dotted
with smaller lakes that range up to 50 kilometers across.
Saturday, December 21
Explanation: Today, the solstice is at 17:11
Universal Time, the Sun reaching the southernmost declination in its yearly
journey through planet Earth's sky. The December solstice marks
the astronomical beginning of winter in the northern hemisphere and summer in
the south. To celebrate, explore this creative visualization of the Sun from
visible to extreme ultraviolet wavelengths, using image data from the orbiting Solar Dynamics Observatory (SDO). Against
a base image made at a visible
wavelengths, the wedge-shaped segments show the solar disk at increasingly
shorter ultraviolet and extreme ultraviolet wavelengths. Shown in false-color
and rotating in a clockwise direction, the filters decrease in wavelength from
170 nanometers (in pink)
through 9.4 nanometers (green). At shorter wavelengths, the altitude and
temperature of the regions revealed in the solar atmosphere tend to increase.
Bright at visible wavelengths, the solar photosphere looks darker in the
ultraviolet, but sunspots
glow and bright plasma
traces looping magnetic fields. Watch the filters sweep around the solar disk
in this
animation of SDO's multiwavelength view of the Sun.
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