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Massive stars in our Milky Way Galaxy live spectacular lives. Collapsing from vast cosmic clouds, their nuclear furnaces ignite and create heavy elements in their cores. After a few million years, the enriched material is blasted back into interstellar space where star formation can begin anew. The expanding debris cloud known as Cassiopeia A is an example of this final phase of the stellar life cycle. Light from the explosion which created this supernova remnant would have been first seen in planet Earth's sky about 350 years ago, although it took that light about 11,000 years to reach us. This false-color Chandra X-ray Observatory image shows the still hot filaments and knots in the Cassiopeia A remnant. High-energy emission from specific elements has been color coded, silicon in red, sulfur in yellow, calcium in green and iron in purple, to help astronomers explore the recycling of our galaxy's star stuff - Still expanding, the blast wave is seen as the blue outer ring. The…

One of the most identifiable nebulae in the sky, the Horsehead Nebula in Orion, is part of a large, dark, molecular cloud. Also known as Barnard 33, the unusual shape was first discovered on a photographic plate in the late 1800s. The red glow originates from hydrogen gas predominantly behind the nebula, ionized by the nearby bright star Sigma Orionis. The darkness of the Horsehead is caused mostly by thick dust, although the lower part of the Horsehead's neck casts a shadow to the left. Streams of gas leaving the nebula are funneled by a strong magnetic field. Bright spots in the Horsehead Nebula's base are young stars just in the process of forming. Light takes about 1,500 years to reach us from the Horsehead Nebula. The featured image was taken with the large 3.6-m Canada-France-Hawaii Telescope in Hawaii, USA. via NASA http://ift.tt/2lcxtbl

Galaxies are fascinating not only for what is visible, but for what is invisible. Grand spiral galaxy NGC 1232, captured in detail by one of the Very Large Telescopes, is a good example. The visible is dominated by millions of bright stars and dark dust, caught up in a gravitational swirl of spiral arms revolving about the center. Open clusters containing bright blue stars can be seen sprinkled along these spiral arms, while dark lanes of dense interstellar dust can be seen sprinkled between them. Less visible, but detectable, are billions of dim normal stars and vast tracts of interstellar gas, together wielding such high mass that they dominate the dynamics of the inner galaxy. Leading theories indicate that even greater amounts of matter are invisible, in a form we don't yet know. This pervasive dark matter is postulated, in part, to explain the motions of the visible matter in the outer regions of galaxies. via NASA http://ift.tt/2ps5tWu

What's happened to the sky? On Friday, the photogenic launch plume from a SpaceX rocket launch created quite a spectacle over parts of southern California and Arizona. Looking at times like a giant space fish, the impressive rocket launch from Vandenberg Air Force Base near Lompoc, California, was so bright because it was backlit by the setting Sun. Lifting off during a minuscule one-second launch window, the Falcon 9 Heavy rocket successfully delivered to low Earth orbit ten Iridium NEXT satellites that are part of a developing global communications network. The plume from the first stage is seen on the right, while the soaring upper stage rocket is seen at the apex of the plume toward the left. Several good videos of the launch were taken. The featured image was captured from Orange County, California, in a 2.5 second duration exposure. via NASA http://ift.tt/2BCAwEL

Based on its well-measured orbit, 3200 Phaethon (sounds like FAY-eh-thon) is recognized as the source of the meteroid stream responsible for the annual Geminid meteor shower. Even though most meteor showers' parents are comets, 3200 Phaethon is a known and closely tracked near-Earth asteroid with a 1.4 year orbital period. Rocky and sun-baked, its perihelion or closest approach to the Sun is well within the orbit of innermost planet Mercury. In this telescopic field of view, the asteroid's rapid motion against faint background stars of the heroic constellation Perseus left a short trail during the two minute total exposure time. The parallel streaks of its meteoric children flashed much more quickly across the scene. The family portrait was recorded near the Geminid meteor shower's very active peak on December 13. That was just before 3200 Phaethon's historic December 16 closest approach to planet Earth. via NASA http://ift.tt/2kZD44i

Welcome to December's solstice, first day of winter in the north and summer for the southern hemisphere. Astronomical markers of the seasons, solstice and equinox dates are based on the Sun's place in its annual journey along the ecliptic, through planet Earth's sky. At this solstice, the Sun reaches its maximum southern declination of -23.5 degrees today at 16:28 UTC, while its right ascension coordinate on the celestial sphere is 18 hours. That puts the Sun in the constellation Sagittarius in a direction near the center of our Milky Way galaxy. In fact, if you could see today's Solstice Sun against faint background stars and nebulae (that's really hard to do, especially in the daytime ...) your view might look something like this composited panorama. To make it, images of our fair galaxy were taken under dark Namibian night skies, then stitched together in a panoramic view. From a snapshot made on December 21, 2015, the Sun was digitally overlayed as a brilliant …

Why is there a spiral around the North Pole of Mars? Each winter this pole develops a new outer layer about one meter thick composed of carbon dioxide frozen out of the thin Martian atmosphere. This fresh layer is deposited on a water-ice layer that exists year round. Strong winds blow down from above the cap's center and swirl due to the spin of the red planet -- contributing to Planum Boreum's spiral structure. The featured image is a perspective mosaic generated earlier this year from numerous images taken by ESA's Mars Express and elevations extracted from the laser altimeter aboard NASA's Mars Global Surveyor mission. New missions to Mars planned in the next few years include Insight with plans to drill into Mars, and ExoMars and the Mars 2020 Rover with plans to search for signs of microscopic Martian life -- past and present. via NASA http://ift.tt/2ATjFch

Most galaxies have a single nucleus -- does this galaxy have four? The strange answer leads astronomers to conclude that the nucleus of the surrounding galaxy is not even visible in this image. The central cloverleaf is rather light emitted from a background quasar. The gravitational field of the visible foreground galaxy breaks light from this distant quasar into four distinct images. The quasar must be properly aligned behind the center of a massive galaxy for a mirage like this to be evident. The general effect is known as gravitational lensing, and this specific case is known as the Einstein Cross. Stranger still, the images of the Einstein Cross vary in relative brightness, enhanced occasionally by the additional gravitational microlensing effect of specific stars in the foreground galaxy. via NASA http://ift.tt/2j8dLNf

Four Geminids flash through northern skies in this wintry night skyscape. The bright fireball and 3 fainter meteors were captured in a single 10 second exposure, near the peak of December's Geminid meteor shower. Reflecting the fireball's greenish light, a partially frozen Lake Edith in Alberta Canada's Jasper National Park lies in the foreground, with the Canadian Rocky Mountains ranging along the northern horizon. Of course, the glacial lake is cold even in summer. But photographer Jack Fusco reports that he experienced -9 degree C temperatures that night while enjoying one of the most active meteor showers he's ever seen. via NASA http://ift.tt/2CyewHQ

Earth's annual Geminid meteor shower did not disappoint as our fair planet plowed through dust from active asteroid 3200 Phaethon. Captured in this northern hemisphere nightscape, the meteors stream away from the shower's radiant in Gemini. To create the image, 37 individual frames recording meteor streaks were taken over period of 8.5 hours during the night of December 12/13. In the final composite they were selected and registered against the starry sky above a radio telescope dish of MUSER, a solar-dedicated radio telescope array at astronomically-named Mingantu Station in Inner Mongolia, China, about 400 kilometers from Beijing. Sirius, alpha star of Canis Major, shines brightly just above the radio dish and the Milky Way stretches toward the zenith. Yellowish Betelgeuse is a standout in Orion to the right of the northen Milky Way. The shower's radiant is at top left, high above the horizon near Castor and Pollux the twin stars of Gemini. The radiant effect is due to p…

What's up in the sky this winter? The featured graphic gives a few highlights for Earth's northern hemisphere. Viewed as a clock face centered at the bottom, early winter sky events fan out toward the left, while late winter events are projected toward the right. Objects relatively close to Earth are illustrated, in general, as nearer to the cartoon figure with the telescope at the bottom center -- although almost everything pictured can be seen without a telescope. Highlights of this winter's sky include the Geminids meteor shower peaking this week, the constellation of Orion becoming notable in the evening sky, and many planets being visible before sunrise in February. As true in every season, the International Space Station (ISS) can be sometimes be found drifting across your sky if you know just when and where to look. via NASA http://ift.tt/2BzDWY7

This composition in stardust covers over 8 degrees on the northern sky. The mosaicked field of view is west of the familiar Pleiades star cluster, toward the zodiacal constellation Aries and the plane of our Milky Way Galaxy. At right in the deep skyscape is bluish Epsilon Arietis, a star visible to the naked-eye and about 330 light-years away. Reflecting starlight in the region, dusty nebulae LBN762, LBN753, and LBN743 sprawl left to right across the field, but are likely some 1,000 light-years away. At that estimated distance, the cosmic canvas is over 140 light-years across. Near the edge of a large molecular cloud, their dark interiors can hide newly formed stars and young stellar objects or protostars from prying optical telescopes. Collapsing due to self-gravity, the protostars form around dense cores embedded in the molecular cloud. via NASA http://ift.tt/2A1Zfx4

December's Full Moon phase occurred near perigee, the closest point in its orbit around our fair planet. Big and bright, the fully illuminated lunar disk sets over rugged mountains in this early morningscape from Turin, Italy. Captured just before sunrise on the opposite horizon, scattered sunlight near the edge of Earth's shadow provides the beautiful reddish glow of the alpine peaks. Hills in the foreground are still in shadow. But the scattered sunlight just illuminates the dome and towers of Turin's historic Basilica of Superga on a hilltop near the lower right in the telephoto frame. via NASA http://ift.tt/2BGwGG3

As seen from planet Earth, all the lunar and solar eclipses of 2017 are represented at the same scale in these four panels. The year's celestial shadow play was followed through four different countries by one adventurous eclipse chaser. To kick off the eclipse season, at top left February's Full Moon was captured from the Czech Republic. Its subtle shading, a penumbral lunar eclipse, is due to Earth's lighter outer shadow. Later that month the New Moon at top right was surrounded by a ring of fire, recorded on film from Argentina near the midpoint of striking annular solar eclipse. The August eclipse pairing below finds the Earth's dark umbral shadow in a partial eclipse from Germany at left, and the vibrant solar corona surrounding a totally eclipsed Sun from the western USA. If you're keeping score, the Saros numbers (eclipse cycles) for all the 2017 eclipses are at bottom left in each panel. via NASA http://ift.tt/2AAbJ0j

To some, it may look like a beehive harboring an evil bee. In reality, the featured Hubble image captures a cosmic pillar of dust, two-light years long, inside of which is Herbig-Haro 666 -- a young star emitting powerful jets. The structure lies within one of our galaxy's largest star forming regions, the Carina Nebula, shining in southern skies at a distance of about 7,500 light-years. The pillar's layered outline are shaped by the winds and radiation of Carina's young, hot, massive stars, some of which are still forming inside the nebula. A dust-penetrating view in infrared light better shows the two, narrow, energetic jets blasting outward from a still hidden infant star. via NASA http://ift.tt/2Bzxqww

What's happening on the horizon? The horizon itself, past a spinach field in Guatemala, shows not only trees but a large volcano: the Volcán de Fuego (Volcano of Fire). The red glow at the top of the volcano is hot lava. But your eye may also be drawn to the blue circle above the horizon on the left. This circle surrounds the Moon and, together with other colors, is called a corona. A corona is caused by diffraction of light -- here moonlight -- by small water droplets in the Earth's intervening atmosphere. A break in the clouds on the right shows stars and even the planet Saturn far beyond the volcano. Although Volcán de Fuego frequently undergoes low-level activity, the astrophotographer considered himself lucky to capture the scene just during an explosive eruption in late September. via NASA http://ift.tt/2klfuTd