Outside

Outside the atmosphere

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Comet 67P from Spacecraft Rosetta

Spacecraft Rosetta continues to circle and map Comet Churyumov-Gerasimenko. Crossing the inner Solar System for ten years to reach the vicinity of the comet in 2014, the robotic spacecraft continues to image the unusual double-lobed comet nucleus. The featured image, taken one year ago, shows dust and gas escaping from the comet's nucleus. Although appearing bright here, the comet's surface reflects only about four percent of impinging visible light, making it as dark as coal. Comet 67P/ChuryumovGerasimenko spans about four kilometers in length and has a surface gravity so low that an astronaut could jump off of it. With Rosetta in tow, Comet 67P passed its closest to the Sun last year and is now headed back to the furthest point -just past the orbit of Jupiter.

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Massive Stars in NGC 6357

Massive stars lie within NGC 6357, an expansive emission nebula complex some 6,500 light-years away toward the tail of the constellation Scorpius. In fact, positioned near center in this ground-based close-up of NGC 6357, star cluster Pismis 24 includes some of the most massive stars known in the galaxy, stars with nearly 100 times the mass of the Sun. The nebula's bright central region also contains dusty pillars of molecular gas, likely hiding massive protostars from the prying eyes of optical instruments. Intricate shapes in the nebula are carved as interstellar winds and energetic radiation from the young and newly forming massive stars clear out the natal gas and dust and power the nebular glow. Enhancing the nebula's cavernous appearance, narrowband image data was included in this composite color image in a Hubble palette scheme. Emission from sulfur, hydrogen, and oxygen atoms is shown in red green and blue hues. The alluring telescopic view spans about 50 light-years at the estimated distance of NGC 6357.

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The Galactic Center in Infrared

The center of our Galaxy is a busy place. In visible light, much of the Galactic Center is obscured by opaque dust. In infrared light, however, dust glows more and obscures less, allowing nearly one million stars to be recorded in the featured photograph. The Galactic Center itself appears on the left and is located about 30,000 light years away towards the constellation of the Archer (Sagittarius). The Galactic Plane of our Milky Way Galaxy, the plane in which the Sun orbits, is identifiable by the dark diagonal dust lane. The absorbing dust grains are created in the atmospheres of cool red-giant stars and grow in molecular clouds. The region directly surrounding the Galactic Center glows brightly in radio and high-energy radiation, and is thought to house a large black hole.

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A Five Planet Dawn

As January closes and in the coming days of February, early morning risers can spot the five naked-eye planets before dawn. Though some might claim to see six planets, in this seaside panoramic view all five celestial wanderers were found above the horizon along with a bright waning gibbous Moon on January 27. Nearly aligned along the plane of the ecliptic, but not along a line with the Sun, the five planets are spread well over 100 degrees across the sky. Just arriving on the predawn scene, fleeting Mercury stands above the southeastern horizon in the golden light of the approaching sunrise.

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NASA Astronomy Picture of the Day 2016 February 3 

Galaxy Wars: M81 versus M82 

In the lower left corner, surrounded by blue spiral arms, is spiral galaxy M81. In the upper right corner, marked by red gas and dust clouds, is irregular galaxy M82. This stunning vista shows these two mammoth galaxies locked in gravitational combat, as they have been for the past billion years. The gravity from each galaxy dramatically affects the other during each hundred million-year pass. Last go-round, M82’s gravity likely raised density waves rippling around M81, resulting in the richness of M81’s spiral arms. But M81 left M82 with violent star forming regions and colliding gas clouds so energetic the galaxy glows in X-rays. This big battle is seen from Earth through the faint glow of an Integrated Flux Nebula, a little studied complex of diffuse gas and dust clouds in our Milky Way Galaxy. In a few billion years only one galaxy will remain.

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The California Nebula

What's California doing in space? Drifting through the Orion Arm of the spiral Milky Way Galaxy, this cosmic cloud by chance echoes the outline of California on the west coast of the United States. Our own Sun also lies within the Milky Way's Orion Arm, only about 1,500 light-years from the California Nebula. Also known as NGC 1499, the classic emission nebula is around 100 light-years long. On the featured image, the most prominent glow of the California Nebula is the red light characteristic of hydrogen atoms recombining with long lost electrons, stripped away (ionized) by energetic starlight. The star most likely providing the energetic starlight that ionizes much of the nebular gas is the bright, hot, bluish Xi Persei just to the right of the nebula. A regular target for astrophotographers, the California Nebula can be spotted with a wide-field telescope under a dark sky toward the constellation of Perseus, not far from the Pleiades.

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Earthset from the Lunar Reconnaissance Orbiter

On the Moon, the Earth never rises -- or sets. If you were to sit on the surface of the Moon, you would see the Earth just hang in the sky. This is because the Moon always keeps the same side toward the Earth. Curiously, the featured image does picture the Earth setting over a lunar edge. This was possible because the image was taken from a spacecraft orbiting the Moon - specifically the Lunar Reconnaissance Orbiter (LRO). In fact, LRO orbits the Moon so fast that, from the spacecraft, the Earth appears to set anew about every two hours. The featured image captured one such Earthset about three months ago. By contrast, from the surface of the Earth, the Moon sets about once a day -- with the primary cause being the rotation of the Earth. LRO was launched in 2009 and, while creating a detailed three dimensional map of the Moon's surface, is also surveying the Moon for water and possible good landing spots for future astronauts.

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Sun Storm: A Coronal Mass Ejection

What's happening to our Sun? Another Coronal Mass Ejection (CME)! The Sun-orbiting SOHO spacecraft has imaged many erupting filaments lifting off the active solar surface and blasting enormous bubbles of magnetic plasma into space. Direct light from the sun is blocked in the inner part of the featured image, taken in 2002, and replaced by a simultaneous image of the Sun in ultraviolet light. The field of view extends over two million kilometers from the solar surface. While hints of these explosive events, called coronal mass ejections or CMEs, were discovered by spacecraft in the early 70s, this dramatic image is part of a detailed record of this CME's development from the presently operating SOHO spacecraft. Near the maximum of the solar activity cycle, CMEs now typically occur several times a week. Strong CMEs may profoundly influence space weather. Those directed toward our planet can have serious effects.

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A Colorful Solar Corona over the Himalayas

What are those colorful rings around the Sun? A corona visible only to Earth observers in the right place at the right time. Rings like this will sometimes appear when the Sun or Moon is seen through thin clouds. The effect is created by the quantum mechanical diffraction of light around individual, similarly-sized water droplets in an intervening but mostly-transparent cloud. Since light of different colors has different wavelengths, each color diffracts differently. Solar Coronae are one of the few quantum color effects that can be easily seen with the unaided eye. This type of solar corona is a visual effect due to water in Earth's atmosphere and is altogether different from the solar corona that exists continually around the Sun -- and stands out during a total solar eclipse. In the foreground is the famous Himalayan mountain peak Ama Dablam (Mother's Necklace).

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A Dark Sand Dune on Mars

What is that dark sand dune doing on Mars? NASA's robotic rover Curiosity has been studying it to find out, making this the first-ever up-close investigation of an active sane dune on another world. Named Namib Dune, the dark sand mound stands about 4 meters tall and, along with the other Bagnold Dunes, is located on the northwestern flank of Mount Sharp. The featured image was taken last month and horizontally compressed here for comprehensibility. Wind is causing the dune to advance about one meter a year across the light bedrock underneath, and wind-blown sand is visible on the left. Part of the Curiosity rover itself is visible on the lower right. Just in the past few days, Curiosity scooped up some of the dark sand for a detailed analysis. After further exploration of the Bagnold Dunes, Curiosity is scheduled to continue its trek up the 5-kilometer tall Mount Sharp, the central peak in the large crater where the car-sized rover landed.

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An Airglow Fan from Lake to Sky

Why would the sky look like a giant fan? Airglow. The featured intermittent green glow appeared to rise from a lake through the arch of our Milky Way Galaxy, as captured last summer next to Bryce Canyon in Utah, USA. The unusual pattern was created by atmospheric gravity waves, ripples of alternating air pressure that can grow with height as the air thins, in this case about 90 kilometers up. Unlike auroras powered by collisions with energetic charged particles and seen at high latitudes, airglow is due to chemiluminescence, the production of light in a chemical reaction. More typically seen near the horizon, airglow keeps the night sky from ever being completely dark.

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Elliptical M60, Spiral NGC 4647

Giant elliptical galaxy M60 and spiral galaxy NGC 4647 do look like an odd couple in this sharp cosmic portrait from the Hubble Space Telescope. But they are found in a region of space where galaxies tend to gather, on the eastern side of the nearby Virgo Galaxy Cluster. About 54 million light-years distant, bright M60's simpler egg-like shape is created by its randomly swarming older stars, while NGC 4647's young blue stars, gas and dust are organized into winding arms rotating in a flattened disk. Spiral NGC 4647 is estimated to be more distant than M60, some 63 million light-years away. Also known as Arp 116, the pair of galaxies may be on the verge of a significant gravitational encounter, though. M60 (aka NGC 4649) is about 120,000 light-years across. The smaller NGC 4647 spans around 90,000 light-years, about the size of our own Milky Way.

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The Fox Fur Nebula

This interstellar canine is formed of cosmic dust and gas interacting with the energetic light and winds from hot young stars. The shape, visual texture, and color, combine to give the region the popular name Fox Fur Nebula. The characteristic blue glow on the left is dust reflecting light from the bright star S Mon, the bright star just below the top edge of the featured image. Textured red and black areas are a combination of the cosmic dust and reddish emission from ionized hydrogen gas. S Mon is part of a young open cluster of stars, NGC 2264, located about 2,500 light years away toward the constellation of the Unicorn (Monoceros).

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Milky Way and Exploding Meteor

Grains of icy rock will streak across the sky as they evaporate during entry into Earth's atmosphere. These grains were shed from Comet Swift-Tuttle. The Perseids result from the annual crossing of the Earth through Comet Swift-Tuttle's orbit, and are typically the most active meteor shower of the year. Although it is hard to predict the level of activity in any meteor shower, in a clear dark sky an observer might see a meteor a minute. This year's Perseids occur just before a new Moon and so the relatively dark sky should make even faint meteors visible. Meteor showers in general are best be seen from a relaxing position, away from lights. Featured here is a meteor caught exploding two weeks ago above Austria next to the central band of our Milky Way Galaxy.

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Eclipsed in Southern Skies

This stunning panorama in southern skies was recorded on the colorful night of September 27/28 from Carngegie Las Campanas Observatory. A diffuse glow and dark rifts of the central Milky Way hang over domes of the twin 6.5 meter Magellan telescopes. But most eye-catching is the deep red glow of the Moon. Immersed in Earth's shadow during the much anticipated perigee-total-lunar eclipse, the Moon's surface reflects the light of sunsets and sunrises scattered and refracted into the planet's cone-shaped umbra. Along with the dramatic hue of the eclipsed Moon, other colors of that night captured by the sensitive digital camera include the red and green shades of atmospheric airglow. Viewers can also spot the Andromeda Galaxy below the Moon, seen as a tiny smudge through the reddish airglow and lights along the horizon. The Magellanic Clouds, satellite galaxies of the Milky Way, join in at the far left of the full panorama frame.

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Sharpless 308: Star Bubble

Blown by fast winds from a hot, massive star, this cosmic bubble is huge. Cataloged as Sharpless 2-308 it lies some 5,200 light-years away toward the constellation of the Big Dog (Canis Major) and covers slightly more of the sky than a Full Moon. That corresponds to a diameter of 60 light-years at its estimated distance. The massive star that created the bubble, a Wolf-Rayet star, is the bright one near the center of the nebula. Wolf-Rayet stars have over 20 times the mass of the Sun and are thought to be in a brief, pre-supernova phase of massive star evolution. Fast winds from this Wolf-Rayet star create the bubble-shaped nebula as they sweep up slower moving material from an earlier phase of evolution. The windblown nebula has an age of about 70,000 years. Relatively faint emission captured in the expansive image is dominated by the glow of ionized oxygen atoms mapped to a blue hue.