Too much time has passed since the
last update. While I have been posting the Astronomy Pictures of the Day to
Twitter, I have been aggregating the pictures on my own. Here’s the series of
astronomy pictures from last week.
Sunday, October 27
Explanation: Arcing toward a
fiery fate, this Sungrazer comet was recorded by the SOHO spacecraft's Large Angle Spectrometric COronagraph(LASCO)
on December 23, 1996. LASCO
uses an occulting disk, partially visible at the lower right, to block out the
otherwise overwhelming solar disk allowing it to image the inner 8 million
kilometers of the relatively faint corona. The comet is seen as
its coma enters the
bright equatorial solar wind
region (oriented vertically). Positioned in space to continuously observe the
Sun, SOHO has now been used to discover over 1,500
comets, including numerous
sungrazers. Based on their orbits, the vast majority of sungrazers are
believed to belong to the Kreutz family of sungrazing
comets created by successive break ups from a single
large parent comet that passed very near the Sun in the twelfth century. The Great Comet of 1965,
Ikeya-Seki, was also a member of the Kreutz family, coming within about
650,000 kilometers of the Sun's surface. Passing so close to the Sun, Sungrazers are
subjected to destructive tidal
forces along with intense solar heat. This small comet, known as the
Christmas Comet SOHO
6, did not survive. Later this year, Comet
ISON, potentially the brightest
sungrazer in recorded history but not a Kreutz sungrazer, is expected to
survive.
Monday, October 28
Illustration Credit: Lieve Verschuier
Explanation: Was there ever
another comet like ISON? Although no two comets are exactly alike, one that
appears to have had notable similarities was Comet Kirch, the Great Comet of 1680.
Like approaching Comet
ISON, Comet
Kirch was a bright sungrazer,
making a very close
approach to the surface of the Sun. Neither comet, coincidently, is a
member of the most common group of sungrazers
-- the Kreutz group
-- populated by remnants of a comet that disintegrated near the Sun
hundreds of years ago. The long tail of Comet Kirch is depicted in
the above painting by Lieve
Versheier. As pictured, some members of the foreground crowd of Rotterdam in the Netherlands are holding
cross-staffs, an angle
measuring device that predated the sextant. No one knows how Comet ISON
will develop, but like Comet Kirch, it is expected to be brightest
when very near the Sun, in ISON's case
during last few days of November.
Tuesday, October 29
Image Credit & Copyright: Roberto
Colombari & Federico Pelliccia
Explanation: The dark Horsehead Nebula and the
glowing Orion Nebula are
contrasting cosmic vistas. Adrift 1,500 light-years away in one of the night sky's most
recognizable constellations,
they appear in opposite corners of the above stunning mosaic. The familiar Horsehead nebula
appears as a dark cloud, a small silhouette notched against the long red glow
at the lower left. Alnitak
is the easternmost star in Orion's
belt and is seen as the brightest star to the left of the Horsehead.
Below Alnitak is the Flame
Nebula, with clouds of bright emission and dramatic dark dust lanes.
The magnificent emission region, the Orion Nebula (aka M42),
lies at the upper right. Immediately to its left is a prominent reflection
nebula sometimes called the Running Man. Pervasive tendrils of glowing hydrogen
gas are easily traced
throughout the region.
Wednesday, October 30
Explanation: Frightening
forms and scary faces are a mark of the Halloween season. They also haunt this cosmic
close-up of the eastern Veil Nebula. The Veil Nebula itself is a
large supernova remnant, the expanding debris cloud from the death explosion of
a massive star. While the Veil is roughly circular in shape covering nearly 3
degrees on the sky in the constellation Cygnus, this portion of the eastern
Veil spans only 1/2 degree, about the apparent size of the Moon. That translates to
12 light-years at the Veil's reassuring estimated distance of 1,400 light-years
from planet Earth. In the composite of image data recorded through narrow band filters,
emission from hydrogen atoms in the remnant is shown in red with strong
emission from oxygen atoms in blue-green hues. In the western part of the Veil
lies another seasonal apparition, the Witch's Broom.
Thursday, October 31
Explanation: What
spooky planet is this? Planet Earth of course, on the dark and stormy night
of September 12 at Hverir, a geothermally active area along the volcanic landscape in
northeastern Iceland. Geomagnetic storms produced the auroral display in the
starry night sky while ghostly towers of steam and gas venting from fumaroles danced
against the eerie greenish light. Tonight, there is still a chance for geomagnetic storms triggered by recent
solar activity, so high-latitude skygazers should beware. And ghostly shapes
may dance in your neighborhood, too. Have a safe and Happy Halloween!
Friday, November 1
Explanation: NGC 7841 is probably
known as the Smoke Nebula, found in the modern constellation of Frustriaus, the
frustrated astrophotographer. Only a few light-nanoseconds from planet Earth, The Smoke
Nebula is not an expanding supernova remnant along the plane of our Milky Way
galaxy, though it does look a
lot like one. Instead it was created by flash photography of rising smoke.
The apparently rich starfield is actually composed of water droplets sprayed
from a plant mister by an astrophotographer grown restless during a recent
stretch of cloudy weather in Sweden. A single exposure and three external
flashes were triggered to capture the not-quite-cosmic
snapshot.
Saturday, November 2
Explanation: This webcam and
telescope image of banded gas giant Jupiter shows the transit of three
shadows cast by Jupiter's moons in progress, captured in Belgian skies on
October 12 at 0528 UT. Such a three shadow transit is a relatively rare event, even
for a large planet with many moons. Visible in the frame are the three
Galilean moons responsible, Callisto
at the far left edge, Io closest
to Jupiter's disk, and
Europa below and just left of Io. Of their shadows on the sunlit Jovian cloud tops, Callisto casts
the most elongated one near the planet's south polar region at the bottom. Io's
shadow is above and right of Jupiter's Great Red Spot. Of course viewed from
Jupiter's perspective, these shadow crossings could be seen as solar eclipses,
analogous to the Moon's
shadow crossing the sunlit face of planet Earth.
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