NASA image of the day (imatge del dia, NASA)

Backdropped by red hills, the Development Motor-2, or DM-2, ignites during an Aug. 31, 2010, static test that was conducted by ATK Aerospace Systems in Promontory, Utah. DM-2, the largest and most powerful solid rocket motor designed for flight, is managed by the Ares Projects Office at NASA's Marshall Space Flight Center in Huntsville, Ala. Image Credit: NASA

Spiral galaxy NGC 4921 presently is estimated to be 320 million light years distant. This image, taken by the Hubble Space Telescope, is being used to identify key stellar distance markers known as Cepheid variable stars. The magnificent spiral NGC 4921 has been informally dubbed anemic because of its low rate of star formation and low surface brightness. Visible in the image are, from the center, a bright nucleus, a bright central bar, a prominent ring of dark dust, blue clusters of recently formed stars, several smaller companion galaxies, unrelated galaxies in the far distant universe, and unrelated stars in our Milky Way Galaxy. Image Credit: NASA, ESA, K. Cook (LLNL)

Is this one galaxy or two? Astronomer Art Hoag first asked this question when he chanced upon this unusual extragalactic object. On the outside is a ring dominated by bright blue stars, while near the center lies a ball of much redder stars that are likely much older. Between the two is a gap that appears almost completely dark. How Hoag's Object formed remains unknown, although similar objects have been identified and collectively labeled as a form of ring galaxy. Genesis hypotheses include a galaxy collision billions of years ago and the gravitational effect of a central bar that has since vanished. This image, taken by the Hubble Space Telescope in July 2001, reveals unprecedented details of Hoag's Object and may yield a better understanding. Hoag's Object spans about 100,000 light years and lies about 600 million light years away toward the constellation of the Snake (Serpens). Coincidentally, visible in the gap (at about one o'clock) is yet another ring galaxy that likely lies far in the distance. Image Credit: NASA, R. Lucas (STScI/AURA)

The picturesque, but snow-capped volcanoes, composing the Islands of the Four Mountains in Alaska's Aleutian Island chain look suspiciously like an alien world in this August 2010 image from the ASTER camera aboard NASA's orbiting Terra satellite. The islands contain restless Mt. Cleveland, an active volcano currently being watched to see if it emits an ash cloud that could affect air travel over parts of North America. A close look at Mt. Cleveland, seen near the image center, shows red vegetation (false color), a white snow-covered peak, a light plume of gas and ash, and dark lanes where ash and debris fell or flowed. Millions of volcanoes have likely been active over the turbulent history of the Earth's surface, while about 20 volcanoes are erupting even today, at any given time. Image Credit: NASA

Cloudless skies allowed a clear view of dust and hydrogen sulfide plumes along the coast of Namibia in early August 2010. The Moderate Resolution Imaging Spectroradiometer (MODIS) on NASA’s Terra satellite captured this natural-color image on Aug. 10, 2010. Multiple dust plumes blow off the coast toward the ocean, most or all of them probably arising from streambeds. Unlike the reddish-tan sands comprising the dunes directly south of the Kuiseb River, the stream-channel sediments are lighter in color. Wind frequently pushes dust plumes seaward along the Namibian Coast. Easterly trade winds blow from the Indian Ocean over the African continent, losing much of their moisture as they go. The winds are hot and dry as they pass over Namibia’s coastal plain, where they are prone to stir fine sediments. Even with dust plumes overhead, the marked change in land cover is obvious along the Kuiseb River. South of the river, sand dunes predominate, but the vegetation along the Kuiseb River prevents the dunes from advancing northward. North of the river, the land surface consists primarily of gravel plains punctuated by rocky hills. Hydrogen sulfide appears as a swath of irridescent green running parallel to the coast north of Walvis Bay. A 2009 study linked the emissions in this region to ocean currents, biological activity in the water column, and carbon-rich organic sediments under the water column. The meeting of hydrogen sulfide gas and oxygen-rich surface waters causes pure sulfur to precipitate into the water. The sulfur’s yellow color makes the water appear green to the satellite sensor. Image Credit: NASA

This image from the Lunar Reconnaissance Orbiter shows the floor of the moon's Anaxagoras crater, including a portion of the crater's anorthositic central uplift. The boulders perched on ridges are eroding out of densely fractured bedrock. This image was taken by the Lunar Reconnaissance Orbiter Camera, or LROC, which consists of a pair of narrow-angle cameras and a single wide-angle camera. The mission is expected to return over 70 terabytes of image data. Image Credit: NASA/GSFC/Arizona State University

Two extremely bright stars illuminate a greenish mist in this image from the Spitzer Space Telescope's "GLIMPSE360" survey. This mist is comprised of hydrogen and carbon compounds called polycyclic aromatic hydrocarbons (PAHs), which also are found here on Earth in sooty vehicle exhaust and on charred grills. In space, PAHs form in the dark clouds that give rise to stars. These molecules provide astronomers a way to visualize the peripheries of gas clouds and study their structures in great detail. They are not actually green; but are color coded in these images to allow scientists see their glow in infrared. This image is a combination of data from Spitzer and the Two-Micron All-Sky Survey (2MASS). The Spitzer data was taken after Spitzer's liquid coolant ran dry in May 2009, marking the beginning of its "warm" mission. Image Credit: NASA/JPL-Caltech/2MASS/SSI/University of Wisconsin

This image shows the eruption of a galactic “super-volcano” in the massive galaxy M87, as witnessed by NASA's Chandra X-ray Observatory and NSF's Very Large Array (VLA). At a distance of about 50 million light years, M87 is relatively close to Earth and lies at the center of the Virgo cluster, which contains thousands of galaxies. The cluster surrounding M87 is filled with hot gas glowing in X-ray light (and shown in blue) that is detected by Chandra. As this gas cools, it can fall toward the galaxy's center where it should continue to cool even faster and form new stars. However, radio observations with the VLA (red) suggest that in M87 jets of very energetic particles produced by the black hole interrupt this process. These jets lift up the relatively cool gas near the center of the galaxy and produce shock waves in the galaxy's atmosphere because of their supersonic speed. The interaction of this cosmic “eruption” with the galaxy's environment is very similar to that of the Eyjafjallajokull volcano in Iceland that occurred in 2010. With Eyjafjallajokull, pockets of hot gas blasted through the surface of the lava, generating shock waves that can be seen passing through the grey smoke of the volcano. This hot gas then rises up in the atmosphere, dragging the dark ash with it. This process can be seen in a movie of the Eyjafjallajokull volcano where the shock waves propagating in the smoke are followed by the rise of dark ash clouds into the atmosphere. In the analogy with Eyjafjallajokull, the energetic particles produced in the vicinity of the black hole rise through the X-ray emitting atmosphere of the cluster, lifting up the coolest gas near the center of M87 in their wake. This is similar to the hot volcanic gases drag up the clouds of dark ash. And just like the volcano here on Earth, shockwaves can be seen when the black hole pumps energetic particles into the cluster gas. Image Credits: X-ray: NASA/CXC/KIPAC/N. Werner et al Radio: NSF/NRAO/AUI/W. Cotton

Making the stuff of science fiction into reality, NASA engineers are testing solar sails--a unique propulsion technology that one day could enable deep space missions. Much like the wind pushing a sailboat through water, solar sails rely on sunlight to propel vehicles through space. The sail captures constantly streaming solar particles, called photons, with giant sails built from a lightweight material. Over time, the buildup of these particles provides enough thrust for a small spacecraft to travel in space. This image is of a four-quadrant solar sail system, measuring 66 feet on each side that is being tested in the world's largest vacuum chamber at NASA's Glenn Research Center at Plum Brook Station in Sandusky, Ohio. Image Credit: NASA

Researchers do not yet know what is lighting up IRAS 05437+2502, a small, faint nebula that spans only 1/18th of a full moon toward the constellation of the Taurus. Particularly enigmatic is the bright upside-down V that defines the upper edge of this floating mountain of interstellar dust. This ghost-like nebula involves a small star-forming region filled with dark dust that was first noted in images taken by the IRAS satellite in infrared light in 1983. This recently released image from the Hubble Space Telescope shows many new details, but has not uncovered a clear cause of the bright sharp arc. Image Credit: NASA, ESA, Hubble, R. Sahai (JPL)

This infrared image taken by NASA's Wide-field Infrared Survey Explorer, or WISE, shows a star-forming cloud teeming with gas, dust and massive newborn stars. WISE, which is surveying the whole sky in infrared light, is particularly sensitive to the warm dust that permeates star-forming clouds like this one. In this way, WISE complements visible-light observations. The mission also complements Hubble and other telescopes by showing the 'big picture," providing context for more detailed observations. The cluster contains some of the most massive stars known. Winds and radiation from the stars are evaporating and dispersing the cloud material from which they formed, warming the cold dust and gas surrounding the central nebula. This greenish "halo" of warm cloud material is seen best by WISE due to its large field of view and improved sensitivity over past all-sky infrared surveys. Image Credit: NASA/JPL-Caltech/UCLA

Reflecting on his experience as he emerged from the craft into the daylight on the Expedition 24 mission's second spacewalk, astronaut Doug Wheelock said "the colors of the Earth just explode at you as you exit toward the planet. Notice what looks like scorch marks on the hatch thermal cover, the effect of vacuum and atomic oxygen on the threads and thread sealant used on the thermal cover. The 'smell' of space follows suit, I’ve heard it described like burnt cake or cookies, or like the smell of an extinguished match." Wheelock and fellow astronaut Tracy Caldwell Dyson completed the second of three spacewalks to remove a failed ammonia coolant pump module on the station's S1 truss on Wednesday, Aug. 11. Image Credit: NASA

Testing advanced designs for high-speed aircraft in 1948, an engineer makes final calibrations to a model mounted in the 6 x 6 Foot Supersonic Wind Tunnel at the NACA Ames Aeronautical Laboratory, Moffett Field, California. NACA, NASA’s predecessor organization the National Advisory Committee for Aeronautics, was established in March 1913 by Congress to "supervise and direct the scientific study of the problems of flight, with a view to their practical solutions." The Ames Aeronautical Laboratory is now NASA’s Ames Research Center. Image Credit: NASA

The idea behind a communications satellite is simple: send a signal into space, and send it back down to another spot on the globe. In NASA's early days, engineers discovered the easiest way to accomplish this: bounce signals off a giant metal balloon floating in orbit. The concept was developed into the aptly-named Echo program, and Echo 1A became the first successful launch of the project on Aug. 12, 1960. Echo 1A, now commonly known as just Echo I, was a 100 foot diameter balloon made of mylar polyester. The spacecraft was designed as a passive communications reflector for transcontinental and intercontinental telephone, radio, and television signals. Pictured here is a scale prototype of the Echo satellite undergoing a Skin Stress Test on May 1, 1960. The prototype was 12 feet in diameter, with the size being chosen because that was the ceiling height in the NASA Langley model shop. After an unsuccessful launch attempt for the original Echo I satellite, Echo 1A and the follow-on Echo II were successfully launched. The Echo projects were instrumental in letting the world see that the U.S. was a major force in the space race not very far behind Russia. Among the many contributions of the Echo programs are the first voice communication via satellite which was made by none other than then President Eisenhower and the first coast-to-coast telephone call using a satellite. In addition, the Echo programs resulted in advances in atmospheric density, solar pressure, gossamer structures, solar sailing, and transmitting videos via satellites. The Echo 1A satellite re-entered the atmosphere on May 24, 1968. Image Credit: NASA

The Centaur Standard Shroud at Glenn Research Center's Space Power Facility, Plum Brook Station, protects spacecraft during launch. When it was constructed, the Space Power Facility was the world's largest vacuum chamber. It stands more than 122 feet high, 100 feet in diameter and provides a vacuum environment for the study of space propulsion. Originally commissioned for nuclear-electric propulsion studies, the SPF has been recommissioned for current and future use in the ongoing research and development of space propulsion systems. Image Credit: NASA

A long-exposure Hubble Space Telescope image shows a majestic face-on spiral galaxy located deep within the Coma Cluster of galaxies, which lies 320 million light- years away in the northern constellation Coma Berenices. The galaxy, known as NGC 4911, contains rich lanes of dust and gas near its center. These are silhouetted against glowing newborn star clusters and iridescent pink clouds of hydrogen, the existence of which indicates ongoing star formation. Hubble has also captured the outer spiral arms of NGC 4911, along with thousands of other galaxies of varying sizes. The high resolution of Hubble's cameras, paired with considerably long exposures, made it possible to observe these faint details. This natural-color Hubble image, which combines data obtained in 2006, 2007, and 2009 from the Wide Field Planetary Camera 2 and the Advanced Camera for Surveys, required 28 hours of exposure time. Image Credit: NASA/ESA/Hubble Heritage Team (STScI/AURA)

Astronaut Leland Melvin waved to the crowds from the NASA Glenn Research Center float during the 2010 Pro Football Hall of Fame Festival Timken Grand Parade on Saturday, August 7, 2010. Melvin is a veteran of two space shuttle flights to the International Space Station and has logged over 565 hours in space. Prior to his selection as an astronaut, he was chosen by the Detroit Lions in the eleventh round of the 1986 National Football League college draft and participated in the Toronto Argonauts and Dallas Cowboys football training camps. Melvin is currently on assignment at NASA Headquarters in Washington, D.C., in support of the Summer of Innovation program. In doing so, he has traveled across the country, engaging thousands of students and teachers in the excitement of space exploration and inspiring them to pursue careers in science, technology, engineering and mathematics, or STEM. The Summer of Innovation initiative is a multi-faceted, intensive middle school program designed to improve STEM teaching and learning in partnership with federal agencies, non profits, industry, and academic and information organizations. Melvin rode on the NASA Glenn Research Center float that depicted the Space Shuttle Discovery. The float won the Janice C. Meyer award for exceptional merit during the parade. Image Credit: NASA/Chris Lynch

On August 1, 2010, almost the entire Earth-facing side of the sun erupted in a tumult of activity. This image from the Solar Dynamics Observatory of the news-making solar event on August 1 shows the C3-class solar flare (white area on upper left), a solar tsunami (wave-like structure, upper right), multiple filaments of magnetism lifting off the stellar surface, large-scale shaking of the solar corona, radio bursts, a coronal mass ejection and more. This multi-wavelength extreme ultraviolet snapshot from the Solar Dynamics Observatory shows the sun's northern hemisphere in mid-eruption. Different colors in the image represent different gas temperatures. Earth's magnetic field is still reverberating from the solar flare impact on August 3, 2010, which sparked aurorae as far south as Wisconsin and Iowa in the United States. Analysts believe a second solar flare is following behind the first flare and could re-energize the fading geomagnetic storm and spark a new round of Northern Lights. Credit: NASA/SDO/AIA

The north polar layered deposits are layers of dusty ice up to 2 miles thick and approximately 620 miles in diameter. We can see the layers exposed on the walls of troughs and scarps cut into the deposits, such as the trough wall imaged here. The bright region at the top is the flat surface above the trough wall; it is higher than the terrain underneath. The wall exposing these layers has a vertical relief of about 1970 feet. It is thought that the north polar layered deposits likely formed recently (i.e., millions of years ago) as rhythmic variations in Mars' orbit changed the distribution of water ice around the planet. As ice moved to and from the polar region in response to a changing climate, layers of ice and dust built up at the poles. By studying the history of these deposits, we hope to understand how the Martian climate has changed, similar to how scientists on Earth study ice cores from the North and South Poles. Three things are immediately apparent about the layers exposed on this trough face. First, individual layers have different surface textures, which some scientists believe could reflect changing physical properties (such as dust content or ice grain size) of the underlying layer. Second, there are several unconformities, or places where one layer is interrupted and overlain by another layer. These unconformities are due to periods where layers were eroded or removed, followed by times when new layers were deposited. Mapping the locations of unconformities can tell us how the deposit shrank and grew over time, and tell us where large changes in climate occurred, causing water ice to be removed from the polar regions. Finally, the dark and bright streaks are due to recent winds blowing surface frost around, and can tell us about wind patterns in the current polar climate. This was imaged by the HiRISE camera onboard the Mars Reconnaissance Orbiter. HiRISE is the most powerful camera of its kind ever sent to another planet. Its high resolution allows us to see Mars like never before and could help other missions choose a safe spot to land for future exploration. Credit: NASA/JPL/University of Arizona

In the Vehicle Assembly Building at NASA's Kennedy Space Center in Florida, workers prepare External Tank-138, hanging vertically in the transfer aisle, for its lift onto a test cell where it will be checked out before launch. ET-138, the last newly manufactured tank, is designated to fly on space shuttle Endeavour's STS-134 mission to the International Space Station. Launch is targeted for Feb. 26, 2011. Credit: NASA/Dimitri Gerondidakis