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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. This image, taken above Hanmer Springs in Canterbury, New Zealand, in 2005, shows great detail partly because sunlight illuminates the undulating...

A supercell is a thunderstorm that is characterized by the presence of a mesocyclone: a deep, persistently rotating updraft. For this reason, these storms are sometimes referred to as rotating thunderstorms. Of the four classifications of thunderstorms (supercell, squall line, multi-cell, and single-cell), supercells are the overall least common and have the potential to be the most severe. Supercells are often isolated from other thunderstorms, and can dominate the local climate up to 32 kilometres (20 mi) away.

Moonlight illuminates a snowy scene in this night land and skyscape made on January 17, 2013 from Lower Miller Creek, Alaska, USA. Overexposed near the mountainous western horizon is the first quarter Moon itself, surrounded by an icy halo and flanked left and right by moondogs. Sometimes called mock moons, a more scientific name for the luminous apparitions is paraselenae (plural). Analogous to a sundog or parhelion, a paraselene is produced by moonlight refracted through thin, hexagonal, plate-shaped ice crystals in high cirrus clouds. As determined by the crystal geometry, paraselenae are seen at an angle of 22 degrees or more from the Moon. Compared to the bright lunar disk, paraselenae are faint and easier to spot when the Moon is low. Image Credit & Copyright: Sebastian Saarloos Explanation: http://apod.nasa.gov/apod/ap130126.html

What's happening above those mountains? Several clouds are stacked up into one striking lenticular cloud. Normally, air moves much more horizontally than it does vertically. Sometimes, however, such as when wind comes off of a mountain or a hill, relatively strong vertical oscillations take place as the air stabilizes. The dry air at the top of an oscillation may be quite stratified in moisture content, and hence forms clouds at each layer where the air saturates with moisture. The result can be a lenticular cloud with a strongly layered appearance. This picture was taken in 2002 looking southwest over the Tararua Range mountains from North Island, New Zealand. Image Credit & Copyright: Chris Picking Explanation from: http://apod.nasa.gov/apod/ap090121.html

This picture was taken during the week of the 2008 summer solstice at Stonehenge in United Kingdom, and captures a picturesque sunrise involving fog, trees, clouds, stones placed about 4,500 years ago, and a 5 billion year old large glowing orb. Even given the precession of the Earth's rotational axis over the millennia, the Sun continues to rise over Stonehenge in an astronomically significant way. Image Credit & Copyright: Max Alexander, STFC, SPL Explanation from: http://apod.nasa.gov/apod/ap100621.html

As magnetic fields on the sun rearrange and realign, dark spots known as sunspots can appear on its surface. Over the course of Feb. 19-20, 2013, scientists watched a giant sunspot form in under 48 hours. It has grown to over six Earth diameters across but its full extent is hard to judge since the spot lies on a sphere not a flat disk. The spot quickly evolved into what's called a delta region, in which the lighter areas around the sunspot, the penumbra, exhibit magnetic fields that point in the opposite direction of those fields in the center, dark area. This is a fairly unstable configuration that scientists know can lead to eruptions of radiation on the sun called solar flares. Image Credit: NASA/SDO/AIA/HMI/Goddard Space Flight Center Explanation from: http://www.nasa.gov/mission_pages/sdo/news/fastgrowing-sunspot.html

NASA's Kepler mission has discovered a new planetary system that is home to the smallest planet yet found around a star like our Sun, approximately 210 light-years away in the constellation Lyra.  The artist's concept depicts the new planet dubbed Kepler-37b. The planet is slightly larger than our Moon, measuring about one-third the size of Earth. Kepler-37b orbits its host star every 13 days at less than one-third the distance Mercury is to the Sun. The estimated surface temperature of this smoldering planet, at more than 800 degrees Fahrenheit (700 degrees Kelvin), would melt the zinc in a penny.  Astronomers don't think the tiny planet has an atmosphere or could support life as we know it, but the Moon-size world is almost certainly rocky in composition.  Image Credit: NASA/Ames/JPL-Caltech Explanation from: http://www.nasa.gov/mission_pages/kepler/multimedia/images/tiny-planet-kepler-37b.html

The ring-like swirls of dust filling the Andromeda Galaxy stand out colorfully in this new image from the Herschel Space Observatory, a European Space Agency mission with important NASA participation.  The glow seen here comes from the longer-wavelength, or far, end of the infrared spectrum, giving astronomers the chance to identify the very coldest dust in our galactic neighbor. These light wavelengths span from 250 to 500 microns, which are a quarter to half of a millimeter in size. Herschel's ability to detect the light allows astronomers to see clouds of dust at temperatures of only a few tens of degrees above absolute zero. These clouds are dark and opaque at shorter wavelengths. The Herschel view also highlights spokes of dust between the concentric rings.  The colors in this image have been enhanced to make them easier to see, but they do reflect real variations in the data. The very coldest clouds are brightest in the longest wavelengths, and colored red here, while th...

One of the Expedition 30 crew members aboard the International Space Station took this nighttime photograph of much of the eastern (Atlantic) coast of the United States. Large metropolitan areas and other easily recognizable sites from the Virginia/Maryland/Washington, D.C. area spanning almost to Rhode Island are visible in the scene. Boston is just out of frame at right. Long Island and the Greater Metropolitan area of New York City are visible in the lower right quadrant. Large cities in Pennsylvania (Philadelphia and Pittsburgh) are near center. Parts of two Russian vehicles parked at the orbital outpost are seen in left foreground. Image Credit: NASA Explanation from: http://www.nasa.gov/mission_pages/station/multimedia/gallery/iss030e078095.html

Two dark shadows loom across the banded and mottled cloud tops of Jupiter in this sharp telescopic view. In fact, captured on January 3, 2013, about a month after the ruling gas giant appeared at opposition in planet Earth's sky, the scene includes the shadow casters. Visible in remarkable detail at the left are the large Galilean moons Ganymede (top) and Io. With the two moon shadows still in transit, Jupiter's rapid rotation has almost carried its famous Great Red Spot (GRS) around the planet's limb from the right. The pale GRS was preceded by the smaller but similar hued Oval BA, dubbed Red Spot Jr., near top center. North is down in the inverted image. Image Credit & Copyright: Damian Peach Explanation from: http://apod.nasa.gov/apod/ap130215.html

This is an image of magnetic loops on the Sun, captured by NASA's Solar Dynamics Observatory (SDO). It has been processed to highlight the edges of each loop to make the structure more clear. A series of loops such as this is known as a flux rope, and these lie at the heart of eruptions on the sun known as coronal mass ejections (CMEs.) This is the first time scientists were able to discern the timing of a flux rope's formation. (Blended 131 Angstrom and 171 Angstrom images of July 19, 2012 flare and CME.) Image Credit: NASA/Goddard Space Flight Center/SDO Explanation from: http://www.nasa.gov/multimedia/imagegallery/image_feature_2451.html

On February 5, 1974, Mariner 10 took this first close-up photo of Venus.  Made using an ultraviolet filter in its imaging system, the photo has been color-enhanced to bring out Venus's cloudy atmosphere as the human eye would see it. Venus is perpetually blanketed by a thick veil of clouds high in carbon dioxide and its surface temperature approaches 900 degrees Fahrenheit. Launched on November 3, 1973 atop an Atlas-Centaur rocket, Mariner 10 flew by Venus in 1974.  Image Credit: NASA Explanation from: http://www.nasa.gov/multimedia/imagegallery/image_feature_2443.html

The giant star Zeta Ophiuchi is having a "shocking" effect on the surrounding dust clouds in this infrared image from NASA’s Spitzer Space Telescope. Stellar winds flowing out from this fast-moving star are making ripples in the dust as it approaches, creating a bow shock seen as glowing gossamer threads, which, for this star, are only seen in infrared light.  Zeta Ophiuchi is a young, large and hot star located around 370 light-years away. It dwarfs our own Sun in many ways -- it is about six times hotter, eight times wider, 20 times more massive, and about 80,000 times as bright. Even at its great distance, it would be one of the brightest stars in the sky were it not largely obscured by foreground dust clouds.  This massive star is travelling at a snappy pace of about 54,000 mph (24 kilometers per second), fast enough to break the sound barrier in the surrounding interstellar material. Because of this motion, it creates a spectacular bow shock ahead of its direction of tra...

The Orion Nebula is featured in this sweeping image from NASA's Wide-field Infrared Survey Explorer, or WISE. The constellation of Orion is prominent in the evening sky throughout the world from about December through April of each year. The nebula (also catalogued as Messier 42) is located in the sword of Orion, hanging from his famous belt of three stars. The star cluster embedded in the nebula is visible to the unaided human eye as a single star, with some fuzziness apparent to the most keen-eyed observers. Because of its prominence, cultures all around the world have given special significance to Orion. The Maya of Mesoamerica envision the lower portion of Orion, his belt and feet (the stars Saiph and Rigel), as being the hearthstones of creation, similar to the triangular three-stone hearth that is at the center of all traditional Maya homes. The Orion nebula, lying at the center of the triangle, is interpreted by the Maya as the cosmic fire of creation surrounded by smoke.  T...

The highly distorted supernova remnant shown in this image may contain themost recent black hole formed in the Milky Way Galaxy. The image combines X-rays from NASA's Chandra X-ray Observatory in blue and green, radio data from the NSF's Very Large Array in pink, and infrared data from Caltech's Palomar Observatory in yellow. The remnant, called W49B, is about a thousand years old, as seen from Earth, and is at a distance of about 26,000 light years away. The supernova explosions that destroy massive stars are generally symmetrical, with the stellar material blasting away more or less evenly in all directions. However, in the W49B supernova, material near the poles of the doomed rotating star was ejected at a much higher speed than material emanating from its equator. Jets shooting away from the star's poles mainly shaped the supernova explosion and its aftermath. By tracing the distribution and amounts of different elements in the stellar debris field, researchers were...

On January 4, 2013 a large presence of stratocumulus clouds was the central focus of camera lenses which remained aimed at the clouds as the Expedition 34 crew members aboard the International Space Station flew above the northwestern Pacific Ocean about 460 miles east of northern Honshu, Japan. This is a descending pass with a panoramic view looking southeast in late afternoon light with the terminator (upper left). The cloud pattern is typical for this part of the world. The low clouds carry cold air over a warmer sea with no discernable storm pattern. Image Credit: NASA Explanation from: http://www.nasa.gov/mission_pages/station/multimedia/gallery/iss034e016601.html

Sometimes, after your eyes adapt to the dark, a spectacular sky appears. Such was the case earlier July 2008 over Ontario, Canada, when part of a spectacular sky also became visible in a reflection off a lake. To start, the brightest objects visible are bright stars and the planet Jupiter, seen as the brightest spot on the upper left. A distant town appears as a diffuse glow over the horizon. More faint still, the disk of the Milky Way Galaxy becomes apparent as a dramatic diffuse band across the sky that seems to crash into the horizon far in the distance. In the foreground, a picturesque landscape includes trees, a lake, and a stone wall. Finally, on this serene night in July when the lake water was unusually calm, reflections appear. Visible in the lake are not only reflections of several bright stars, but part of the Milky Way band itself. Careful inspection of the image will reveal, however, that bright stars leave small trails in the lake reflections that do not appear in the sky...

Sculpted by stellar winds and radiation, a magnificent interstellar dust cloud by chance has assumed this recognizable shape. Fittingly named the Horsehead Nebula, it is some 1,500 light-years distant, embedded in the vast Orion cloud complex. About five light-years "tall", the dark cloud is cataloged as Barnard 33 and is visible only because its obscuring dust is silhouetted against the glowing red emission nebula IC 434. Contrasting blue reflection nebula NGC 2023 is visible on the lower left. In this gorgeous color image, both Horsehead and NGC 2023 seem to be caught in beams of light shining from above - but the beams are actually just internal reflections from bright star Sigma Orionis, just off the upper edge of the view. Image Credit & Copyright: Daniel Verschatse Explanation from: http://apod.nasa.gov/apod/ap051130.html

Apollo 11, Orbit of the Moon July 24, 1969 : Images Credit: NASA

Why would clouds appear to be different colors? The reason here is that ice crystals in distant cirrus clouds are acting like little floating prisms. Sometimes known as a fire rainbow for its flame-like appearance, a circumhorizon arc lies parallel to the horizon. For a circumhorizontal arc to be visible, the Sun must be at least 58 degrees high in a sky where cirrus clouds are present. Furthermore, the numerous, flat, hexagonal ice-crystals that compose the cirrus cloud must be aligned horizontally to properly refract sunlight in a collectively similar manner. Therefore, circumhorizontal arcs are quite unusual to see. This circumhorizon display was photographed through a polarized lens above Dublin, Ohio in May 2009. Image Credit & Copyright: Todd Sladoje Explanation from: http://apod.nasa.gov/apod/ap090512.html

What's happening over the horizon? Although the scene may appear somehow supernatural, nothing more unusual is occurring than a setting Sun and some well placed clouds. In this picture are anticrepuscular rays. To understand them, start by picturing common crepuscular rays that are seen any time that sunlight pours though scattered clouds. Now although sunlight indeed travels along straight lines, the projections of these lines onto the spherical sky are great circles. Therefore, the crepuscular rays from a setting (or rising) sun will appear to re-converge on the other side of the sky. At the anti-solar point 180 degrees around from the Sun, they are referred to as anticrepuscular rays. On this picture is a particularly striking set of anticrepuscular rays photographed in 2001 from a moving car just outside of Boulder, Colorado, USA. Image Credit & Copyright: John Britton Explanation from: http://apod.nasa.gov/apod/ap101128.html

Santa Fe, New Mexico, USA Image Credit & Copyright: Robert Hanelt

In 2011 it was one of the most memorable auroras of the season. There was green light, red light, and sometimes a mixture of the two. There were multiple rays, distinct curtains, and even an auroral corona. It took up so much of the sky. In the background were stars too numerous to count, in the foreground a friendtrying to image the same sight. The scene was captured with a fisheye lens around and above Tromsø, Norway, in November 2011. With the Sun becoming more active, this year might bring even more spectacular aurora. Image Credit & Copyright: Ole Christian Salomonsen Explanation from: http://apod.nasa.gov/apod/ap111205.html