Can one galaxy hide behind another? Not in the case of SDP.81. Here the foreground galaxy, shown in blue in an image taken by the Hubble Space Telescope, acts like a huge gravitational lens, pulling light from a background galaxy, shown in red in an image taken in radio waves by the Atacama Large Millimeter Array (ALMA), around it, keeping it visible. The alignment is so precise that the distant galaxy is distorted into part of a ring around the foreground galaxy, a formation known as an Einstein ring. Detailed analysis of the gravitational lens distortions indicate that a small dark satellite galaxy participates in the deflections, bolstering indication that many satellite galaxies are quite dim and dominated by dark matter. That small galaxy is depicted by a small white dot on the left. Although spanning only a few arcseconds, the featured Einstein ring is really tens of thousands of light years across.

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What kind of clouds are these? Although their cause is presently unknown, such unusual atmospheric structures, as menacing as they might seem, do not appear to be harbingers of meteorological doom. Known informally as Undulatus asperatus clouds, they can be stunning in appearance, unusual in occurrence, are relatively unstudied, and have even been suggested as a new type of cloud. Whereas most low cloud decks are flat bottomed, asperatus clouds appear to have significant vertical structure underneath. Speculation therefore holds that asperatus clouds might be related to lenticular clouds that form near mountains, or mammatus clouds associated with thunderstorms, or perhaps a foehn wind — a type of dry downward wind that flows off mountains. Such a wind called the Canterbury arch streams toward the east coast of New Zealand’s South Island. The featured image, taken above Hanmer Springs in Canterbury, New Zealand, in 2005, shows great detail partly because sunlight illuminates the undulating clouds from the side.

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Want to take a fast trip to the edge of the Solar System? Consider a ride on a Heliopause Electrostatic Rapid Transit System (HERTS). The concept is currently being tested and it might take only 10 to 15 years to make the trip of over 100 Astronomical Units (15 billion kilometers). That’s fast compared to the 35 years it took Voyager 1, presently humanity’s most distant spacecraft, to approach the heliopause or outer boundary of the influence of the solar wind. HERTS would use an advanced electric solar sail that works by extending multiple, 20 kilometer or so long, 1 millimeter thin, positively charged wires from a rotating spacecraft. The electrostatic force generated repels fast moving solar wind protons to create thrust. Compared to a reflective solar light sail, another propellantless deep space propulsion system, the electric solar wind sail could continue to accelerate at greater distances from the Sun, still developing thrust as it cruised toward the outer planets.

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Innermost planet Mercury and a thin crescent Moon are never found far from the Sun in planet Earth’s skies. Taken near dusk on April 8, this colorful evening skyscape shows them both setting toward the western horizon just after the Sun. The broad Tagus River and city lights of Lisbon, Portugal run through the foreground under the serene twilight sky. Near perigee or closest approach to Earth, the Moon’s bright, slender crescent represents about 3 percent of the lunar disk in sunlight. Of course as seen from the Moon, a nearly full Earth would light up the lunar night, and that strong perigee earthshine makes the rest of the lunar disk visible in this scene. Bright Mercury stays well above the western horizon at sunset for northern skywatchers in the coming days. The fleeting planet reaches maximum elongation, or angular distance from the Sun, on April 18. But Mercury will swing back toward the Sun and actually cross the solar disk on May 9, the first transit of Mercury since November 8, 2006.

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Inner planet Venus and a thin crescent Moon are never found far from the Sun in planet Earth’s skies. Taken near dawn on April 6, this timelapse composite shows them both rising just before the Sun. The mountaintop Teide Observatory domes on the fortunate island of Tenerife appear in silhouette against the twilight. In fact, the series of telephoto exposures follows the occultation of Venus by the Moon in three frames. Far from Earth in its orbit and in a nearly full phase, Venus was 96 percent illuminated. Near perigee or closest approach to Earth, the Moon’s slender crescent represents about 2 percent of the lunar disk in sunlight. Seen in the first two exposures, the brilliant morning star only vanishes in the third as it winks out behind the bright lunar limb. Five minutes of the dramatic occultation at dawn is compressed into 15 seconds in this timelapse video (vimeo).

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When did Orion become so flashy? This colorful rendition of part of the constellation of Orion comes from red light emitted by hydrogen and sulfur (SII), and blue-green light emitted by oxygen (OIII). Hues on the featured image were then digitally reassigned to be indicative of their elemental origins — but also striking to the human eye. The breathtaking composite was painstakingly composed from hundreds of images which took nearly 200 hours to collect. Pictured, Barnard’s Loop, across the image bottom, appears to cradle interstellar constructs including the intricate Orion Nebula seen just right of center. The Flame Nebula can also be quickly located, but it takes a careful eye to identify the slight indentation of the dark Horsehead Nebula. As to Orion’s flashiness — a leading explanation for the origin of Barnard’s Loop is a supernova blast that occurred about two million years ago.

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Sometimes, a total eclipse is a good time to eye the Sun. Taking advantage of an unusual juxtaposition of Earth, Moon and Sun, the featured image depicts the total solar eclipse that occurred last month as it appeared — nearly simultaneously — from both Earth and space. The innermost image shows the total eclipse from the ground, with the central pupil created by the bright Sun covered by a comparatively dark Moon. Surrounding the blocked solar disk is the tenuous corona of Sun imaged in white light, easily visible from the ground only during an eclipse. Normally, this corona is hard to track far from the Sun, but the featured montage matches it to false-colored observations of the Sun from NASA and ESA‘s space-based, Sun-orbiting, Solar and Heliospheric Observatory (SOHO). Observations like this allow the study of the constantly changing magnetic activity both near and far from the Sun, the same activity that ultimately drives Earth’s auroras.

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Comet Linear has become unexpectedly bright. The comet, discovered in 2000, underwent a 100-fold outburst just a week before it passed a mere 14 lunar distances from Earth late last month. The comet was captured here last week at about magnitude 6 — just bright enough to be seen by the unaided eye — passing in front of the distant globular star cluster M14. Comet 252/P LINEAR is one of a rare group of comets that vacillate between the Earth and Jupiter every 5 years. How the comet will evolve from here is unknown, but hopes run high that it will remain a good object for binoculars in northern skies for the next week or two.

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Cassini, a robot spacecraft launched in 1997 by NASA, became close enough in 2002 to resolve many rings and moons of its destination planet: Saturn. At that time, Cassini snapped several images during an engineering test. Several of those images were combined into the contrast-enhanced color composite featured here. Saturn’s rings and cloud-tops are visible toward the image bottom, while Titan, its largest moon, is visible as the speck toward the top. When arriving at Saturn in July 2004, the Cassini orbiter began to circle and study the Saturnian system. A highlight was when Cassini launched the Huygens probe that made an unprecedented landing on Titan in 2005, sending back detailed pictures. Now nearing the end of its mission, Cassini is scheduled to embark on a Grand Finale phase in late 2016 where it will repeatedly dive between the giant planet and its innermost rings.

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Taken on March 20 from the top of Haleakala on the isle of Maui, planet Earth, the first sunrise of northern spring is pictured in this vacation snapshot. The telephoto view from the volcanic caldera above a sea of clouds also captures an elusive green flash near the Sun’s upper limb. Atmospheric layers with sharp temperature changes cause the colorful flash as the Sun rises behind a distant cloud bank. Refraction along sight lines through the layers creates multiple distorted images of the Sun, and for a moment, can visibly deflect shorter wavelength green light.

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