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Sentinels of the Arctic

Who guards the north? Judging from this photograph, possibly giant trees covered in snow and ice. The picture was taken in 2011 in Finnish Lapland where weather can include sub-freezing temperatures and driving snow. Surreal landscapes sometimes result, where common trees become cloaked in white and so appear, to some, as watchful aliens. Far in the distance, behind this uncommon Earthly vista, is a more common sight - a Belt of Venus that divided a darkened from sunlit sky as the Sun rose behind the photographer. Of course, in the spring, the trees have thawed and Lapland looks much different.

Image Credit & Copyright: Niccolò Bonfadini
Explanation from: http://apod.nasa.gov/apod/ap120529.html

Pink Aurora over Crater Lake

Why is this aurora strikingly pink? When photographing picturesque Crater Lake in Oregon, USA in June 2012, the background sky lit up with auroras of unusual colors. Although much is known about the physical mechanisms that create auroras, accurately predicting the occurrence and colors of auroras remains a topic of investigation. Typically, it is known, the lowest auroras appear green. These occur at about 100 kilometers high and involve atmospheric oxygen atoms excited by fast moving plasma from space. The next highest auroras -- at about 200 kilometers up -- appear red, and are also emitted by resettling atmospheric oxygen. Some of the highest auroras visible -- as high as 500 kilometers up -- appear blue, and are caused by sunlight-scattering nitrogen ions. When looking from the ground through different layers of distant auroras, their colors can combine to produce unique and spectacular hues, in this case rare pink hues seen above. As Solar Maximum nears in 2013, particle explosions from the Sun are sure to continue and likely to create even more memorable nighttime displays.

Image Credit & Copyright: Brad Goldpaint
Explanation from: http://apod.nasa.gov/apod/ap120725.html

Volcano and Aurora in Iceland

Sometimes both heaven and Earth erupt. In Iceland in 1991, the volcano Hekla erupted at the same time that auroras were visible overhead. Hekla, one of the most famous volcanoes in the world, has erupted at least 20 times over the past millennium, sometimes causing great destruction. The last eruption occurred only twelve years ago but caused only minor damage. The green auroral band occurred fortuitously about 100 kilometers above the erupting lava.

Image Credit & Copyright: Sigurdur H. Stefnisson
Explanation from: http://apod.nasa.gov/apod/ap120708.html

Otherworldly Planet Rise

What would a sunrise look like on another world? So far, humanity has only recorded sunrises on Mars and Earth, but it is fun to wonder what they would look like on planets known and yet unknown. Planets far from their parent star would record the rise of an unusually bright point of light rather than a round orb. Although this might appear to be what is on this picture, the careful combination of long exposures and creative lighting is actually based on Venus-rise from planet Earth, captured through Mesa Arch in Canyonlands National Park, Utah, USA. Picturesque buttes and mesas dot the background landscape. The orange sky is created by air scattering and dust, but is likely reminiscent of dusty skyscapes on Mars.

Image Credit & Copyright: Robert Arn
Explanation from: http://apod.nasa.gov/apod/ap110411.html

Milky Way above Easter Island

Why were the statues on Easter Island built? No one is sure. What is sure is that over 800 large stone statues exist there. The Easter Island statues, stand, on the average, over twice as tall as a person and have over 200 times as much mass. Few specifics are known about the history or meaning of the unusual statues, but many believe that they were created about 500 years ago in the images of local leaders of a lost civilization. In this picture, some of the stone giants were illuminated in 2009 under the central band of our Milky Way Galaxy.

Image Credit & Copyright: Manel Soria
Explanation from: http://apod.nasa.gov/apod/ap120618.html

A Quadruple Lunar Halo over Spain

Sometimes falling ice crystals make the atmosphere into a giant lens causing arcs and halos to appear around the Sun or Moon. Near Madrid, Spain, where a winter sky displayed not only a bright Moon but as many as four rare lunar halos. The brightest object, near the top of the above image, is the Moon. Light from the Moon refracts through tumbling hexagonal ice crystals into a 22 degree halo seen surrounding the Moon. Elongating the 22 degree arc horizontally is a circumscribed halo caused by column ice crystals. More rare, some moonlight refracts through more distant tumbling ice crystals to form a (third) rainbow-like arc 46 degrees from the Moon and appearing here just above a picturesque winter landscape. Furthermore, part of a whole 46 degree circular halo is also visible, so that an extremely rare - especially for the Moon - quadruple halo was actually imaged. The snow-capped trees in the foreground line the road Puerto de Navacerrada in the Sierra de Guadarrama mountain range near Madrid. Far in the background is a famous winter skyscape that includes Sirius, the belt of Orion, and Betelgeuse all visible between the inner and outer arcs. Halos and arcs typically last for minutes to hours, so if you do see one there should be time to invite family, friends or neighbors to share your unusual lensed vista of the sky.

Image Credit & Copyright: Dani Caxete
Explanation from: http://apod.nasa.gov/apod/ap121203.html

Ash and Lightning above Eyjafjallajökull Volcano

Suðurland, Iceland

Image Credit & Copyright: Sigurður Hrafn Stefnisson

Sarychev Peak Eruption seen from the International Space Station

A fortuitous orbit of the International Space Station allowed the astronauts this striking view of Sarychev Volcano (Kuril Islands, northeast of Japan) in an early stage of eruption on June 12, 2009. Sarychev Peak is one of the most active volcanoes in the Kuril Island chain, and it is located on the northwestern end of Matua Island. Prior to June 12, the last explosive eruption occurred in 1989, with eruptions in 1986, 1976, 1954, and 1946 also producing lava flows. Ash from the multi-day eruption has been detected 2,407 kilometers east-southeast and 926 kilometers west-northwest of the volcano, and commercial airline flights are being diverted away from the region to minimize the danger of engine failures from ash intake.

This detailed astronaut photograph is exciting to volcanologists because it captures several phenomena that occur during the earliest stages of an explosive volcanic eruption. The main column is one of a series of plumes that rose above Matua Island on June 12. The plume appears to be a combination of brown ash and white steam. The vigorously rising plume gives the steam a bubble-like appearance.

In contrast, the smooth white cloud on top may be water condensation that resulted from rapid rising and cooling of the air mass above the ash column. This cloud, which meteorologists call a pileus cloud, is probably a transient feature: the eruption plume is starting to punch through. The structure also indicates that little to no shearing wind was present at the time to disrupt the plume. (Satellite images acquired 2-3 days after the start of activity illustrate the effect of shearing winds on the spread of the ash plumes across the Pacific Ocean.)

By contrast, a cloud of denser, gray ash—probably a pyroclastic flow—appears to be hugging the ground, descending from the volcano summit. The rising eruption plume casts a shadow to the northwest of the island (image top). Brown ash at a lower altitude of the atmosphere spreads out above the ground at image lower left. Low-level stratus clouds approach Matua Island from the east, wrapping around the lower slopes of the volcano. Only about 1.5 kilometers of the coastline of Matua Island (image lower center) are visible beneath the clouds and ash.

Image Credit: NASA
Explanation from: http://earthobservatory.nasa.gov/NaturalHazards/view.php?id=38985

Aurora and Geminid Meteor over Kirkjufell

Kirkjufell, Iceland

December 15, 2012

Image Credit & Copyright: David Clapp

Geminids over Kitt Peak

Two large telescope domes stand in the foreground of this night sky view from Kitt Peak National Observatory, near Tucson, Arizona, USA. The dramatic scene was recorded in 2010 near the peak of December's Geminid Meteor Shower. With dome slit open, the building closest to the camera houses the 2.3 Meter (90 inch) Bok Telescope operated by Steward Observatory, University of Arizona. Behind the Bok is the Mayall 4 Meter telescope dome. Of course, no telescopes were needed to enjoy the meteors streaking through the sky! The composite image consists of 13 exposures each 15 seconds long, taken with a wide angle lens over a period of about 2 hours during Kitt Peak's warm, clear, night. An annual celestial event, this meteor shower is the result of planet Earth plowing through dust from mysterious, asteroid-like object 3200 Phaethon.

Image Credit & Copyright: David A. Harvey
Explanation from: http://apod.nasa.gov/apod/ap101216.html

On the road to Carina

This rugged road through the dark Atacama Desert seems to lead skyward toward the bright stars and glowing nebulae of the southern Milky Way. If you follow the road you will get to Cerro Armazones peak in Chile, future construction site for the 40-meter class European Extremely Large Telescope. The scene is dominated by the reddish glow of the Carina Nebula, one of our galaxy's largest star forming regions. In fact, the remarkable skyscape is not a composite of varying exposures or a photomontage. Far from sources of light pollution, the landscape illuminated by starlight and the Milky Way above were recorded by a modified digital camera and fast lens. The sensitive system captured both planet Earth and deep sky in a relatively short exposure.

Image Credit & Copyright: Babak Tafreshi
Explanation from: http://apod.nasa.gov/apod/ap120218.html

Earthrise - 24 December 1968

The rising Earth is about five degrees above the lunar horizon in this telephoto view taken from the Apollo 8 spacecraft near 110 degrees east longitude. The horizon, about 570 kilometers (350 statute miles) from the spacecraft, is near the eastern limb of the moon as viewed from Earth. Width of the view at the horizon is about 150 kilometers (95 statute miles). On Earth 240,000 statute miles away the sunset terminator crosses Africa. The crew took the photo around 10:40 a.m. Houston time on the morning of December 24, and that would make it 15:40 GMT on the same day. The South Pole is in the white area near the left end of the terminator. North and South America are under the clouds.

Image Credit: NASA
Explanation from: http://spaceflight.nasa.gov/gallery/images/apollo/apollo8/html/as08-14-2383.html

Gas Pillars in the Eagle Nebula (M16): Pillars of Creation in a Star-Forming Region

Undersea corral? Enchanted castles? Space serpents? These eerie, dark pillar-like structures are actually columns of cool interstellar hydrogen gas and dust that are also incubators for new stars. The pillars protrude from the interior wall of a dark molecular cloud like stalagmites from the floor of a cavern. They are part of the "Eagle Nebula" (also called M16 — the 16th object in Charles Messier's 18th century catalog of "fuzzy" objects that aren't comets), a nearby star-forming region 6,500 light-years away in the constellation Serpens.

The pillars are in some ways akin to buttes in the desert, where basalt and other dense rock have protected a region from erosion, while the surrounding landscape has been worn away over millennia. In this celestial case, it is especially dense clouds of molecular hydrogen gas (two atoms of hydrogen in each molecule) and dust that have survived longer than their surroundings in the face of a flood of ultraviolet light from hot, massive newborn stars (off the top edge of the picture). This process is called "photoevaporation. "This ultraviolet light is also responsible for illuminating the convoluted surfaces of the columns and the ghostly streamers of gas boiling away from their surfaces, producing the dramatic visual effects that highlight the three-dimensional nature of the clouds. The tallest pillar (left) is about about 4 light-years long from base to tip.

As the pillars themselves are slowly eroded away by the ultraviolet light, small globules of even denser gas buried within the pillars are uncovered. These globules have been dubbed "EGGs." EGGs is an acronym for "Evaporating Gaseous Globules," but it is also a word that describes what these objects are. Forming inside at least some of the EGGs are embryonic stars — stars that abruptly stop growing when the EGGs are uncovered and they are separated from the larger reservoir of gas from which they were drawing mass. Eventually, the stars themselves emerge from the EGGs as the EGGs themselves succumb to photoevaporation.

The picture was taken on April 1, 1995 with the Hubble Space Telescope Wide Field and Planetary Camera 2. The color image is constructed from three separate images taken in the light of emission from different types of atoms. Red shows emission from singly-ionized sulfur atoms. Green shows emission from hydrogen. Blue shows light emitted by doubly- ionized oxygen atoms.

Image Credit: NASA, ESA, STScI, J. Hester and P. Scowen
Explanation from: http://hubblesite.org/newscenter/archive/releases/1995/44/image/a/

Solar Minimum and Solar Maximum

The Sun goes through a natural solar cycle approximately every 11 years. The cycle is marked by the increase and decrease of sunspots - visible as dark blemishes on the Sun's surface, or photosphere. The greatest number of sunspots in any given solar cycle is designated as "solar maximum." The lowest number is "solar minimum."

The solar cycle provides more than just increased sunspots, however. In the Sun's atmosphere, or corona, bright active regions appear, which are rooted in the lower sunspots. Scientists track the active regions since they are often the origin of eruptions on the Sun such as solar flares or coronal mass ejections.

The most recent solar minimum occurred in 2008, and the Sun began to ramp up in January 2010, with an M-class flare (a flare that is 10 times less powerful than the largest flares, labeled X-class). The Sun has continued to get more active, with the next solar maximum predicted for 2013.

The journey toward solar maximum is evident in current images of the Sun, showing a marked difference from those of 2010, with bright active regions dotted around the star.

Image Credit: NASA/SDO
Explanation from: http://www.nasa.gov/mission_pages/sunearth/news/solarmin-max.html

End of the Earth - Created by humans in 21 pictures

Aurora over Laksaa

Laksaa, Nordland Fylke, Norway

January 22, 2012

Image Credit & Copyright: Arild Heitmann

Dust Pillars in the Carina Nebula

These one-light-year-tall pillars of cold hydrogen and dust, imaged by the Hubble Space Telescope, are located in the Carina Nebula. Violent stellar winds and powerful radiation from massive stars are sculpting the surrounding nebula. Inside the dense structures, new stars may be born.

This image of dust pillars in the Carina Nebula is a composite of 2005 observations taken of the region in hydrogen light (light emitted by hydrogen atoms) along with 2010 observations taken in oxygen light (light emitted by oxygen atoms), both times with Hubble's Advanced Camera for Surveys. The immense Carina Nebula is an estimated 7,500 light-years away in the southern constellation Carina.

Image Credit:NASA, ESA, and the Hubble Heritage Project (STScI/AURA)
Explanation from: http://hubblesite.org/newscenter/archive/releases/2010/29/image/a/

Moon, Jupiter and Moons

Skygazers around planet Earth enjoyed the close encounter of planets and Moon in July 15's predawn skies. And while many saw bright Jupiter next to the slender, waning crescent, Europeans also had the opportunity to watch the ruling gas giant pass behind the lunar disk, occulted by the Moon as it slid through the night. Clouds threaten in this telescopic view from Montecassiano, Italy, but the frame still captures Jupiter after it emerged from the occultation along with all four of its large Galilean moons. The sunlit crescent is overexposed with the Moon's night side faintly illuminated by Earthshine. Lined up left to right beyond the dark lunar limb are Callisto, Ganymede, Jupiter, Io, and Europa. In fact, Callisto, Ganymede, and Io are larger than Earth's Moon, while Europa is only slightly smaller.

Image Credit & Copyright: Cristian Fattinnanzi
Explanation from: http://apod.nasa.gov/apod/ap120720.html

Milky Way Galaxy seen over Mount Rainier

Mount Rainier, Olympic Peninsula, Washington

October, 2012

Image Credit & Copyright: Dave Morrow

Mars and a Colorful Lunar Fog Bow

Even from the top of a volcanic crater, this vista was unusual. For one reason, Mars was dazzlingly bright in January 2010, when this picture was taken, as it was nearing its brightest time of the entire year. Mars, on the far upper left, is the brightest object in this picture. The brightness of the red planet peaked last week near when Mars reached opposition, the time when Earth and Mars are closest together in their orbits. Arching across the lower part of the image is a rare lunar fog bow. Unlike a more commonly seen rainbow, which is created by sunlight reflected prismatically by falling rain, this fog bow was created by moonlight reflected by the small water drops that compose fog. Although most fog bows appear white, all of the colors of the rainbow were somehow visible here. This image was taken from high atop Haleakala, a huge volcano in Hawaii, USA.

Image Credit & Copyright: Wally Pacholka
Explanation from: http://apod.nasa.gov/apod/ap100202.html

Two Earth's Satellites viewed from Houston

This photograph taken from Houston, Texas, juxtaposes Earth’s oldest satellite with one of its youngest. The Moon is thought to have been formed by the impact of a large body (perhaps Mars-sized) with the early Earth approximately 4.6 billion years ago. In contrast, the first components of the International Space Station (ISS) assumed orbit around the Earth in 1998, with assembly completed 13 years later—a significant period of time to us, but the merest fraction of a second in the history of the Moon.

While the ISS appears to be fairly close to the Moon’s surface in the image, it’s a trick of perspective. The Moon orbits Earth at an average distance of 384,400 kilometers (238,855 miles), while the ISS orbits at altitudes ranging from approximately 330 to 410 kilometers (205 to 255 miles).

The ISS can frequently be viewed from the Earth’s surface with the naked eye as a bright object moving rapidly across the sky. The ISS has also been photographed from Earth transiting more dramatic backdrops, such as the Sun.

As can be seen in the high-resolution version of this image, major structural elements of the Station—such as the solar panel arrays—can be resolved using high-powered binoculars or lenses. Major features of the lunar nearside surface are likewise discernable with the naked eye, the most obvious being the dark maria lowlands (mare in plural) contrasting with the bright highland regions (or terrae). With moderate magnification, other features such as impact craters become clearly visible; for example, Copernicus and Tycho Craters.

Image Credit: NASA
Explanation from: http://earthobservatory.nasa.gov/IOTD/view.php?id=76942

Eta Carinae: A Star on the Brink of Destruction

A huge, billowing pair of gas and dust clouds are captured in this stunning NASA Hubble Space Telescope image of the supermassive star Eta Carinae.

Using a combination of image processing techniques (dithering, subsampling and deconvolution), astronomers created one of the highest resolution images of an extended object ever produced by the Hubble Space Telescope. The resulting picture reveals astonishing detail.

Even though Eta Carinae is more than 8,000 light-years away, structures only 10 billion miles across (about the diameter of our solar system) can be distinguished. Dust lanes, tiny condensations, and strange radial streaks all appear with unprecedented clarity.

Eta Carinae was observed by Hubble in September 1995 with the Wide Field Planetary Camera 2 (WFPC2). Images taken through red and near-ultraviolet filters were subsequently combined to produce the color image shown. A sequence of eight exposures was necessary to cover the object's huge dynamic range: the outer ejecta blobs are 100,000 times fainter than the brilliant central star.

Eta Carinae was the site of a giant outburst about 150 years ago, when it became one of the brightest stars in the southern sky. Though the star released as much visible light as a supernova explosion, it survived the outburst. Somehow, the explosion produced two polar lobes and a large thin equatorial disk, all moving outward at about 1.5 million miles per hour.

The new observation shows that excess violet light escapes along the equatorial plane between the bipolar lobes. Apparently there is relatively little dusty debris between the lobes down by the star; most of the blue light is able to escape. The lobes, on the other hand, contain large amounts of dust which preferentially absorb blue light, causing the lobes to appear reddish.

Estimated to be 100 times more massive than our Sun, Eta Carinae may be one of the most massive stars in our Galaxy. It radiates about five million times more power than our Sun. The star remains one of the great mysteries of stellar astronomy, and the new Hubble images raise further puzzles. Eventually, this star's outburst may provide unique clues to other, more modest stellar bipolar explosions and to hydrodynamic flows from stars in general.

Image Credit: NASA, ESA, Jon Morse, J. Hester
Explanation from: http://hubblesite.org/newscenter/archive/releases/1996/23/image/a/

Night-Shining Clouds are Getting Brighter

After the Sun sets on a summer evening and the sky fades to black, you may be lucky enough to see thin, wavy clouds illuminating the night, such as these seen over Billund, Denmark, on July 15, 2010. Noctilucent or polar mesospheric clouds, form at very high altitudes—between 80 and 85 kilometers (50–53 miles)—which positions them to reflect light long after the Sun has dropped below the horizon. These “night-shining” clouds are rare—rare enough that Matthew DeLand, who has been studying them for 11 years, has only seen them once in person. But the chances of seeing these elusive clouds are increasing.

DeLand, an atmospheric scientist with Science Systems and Applications Inc. and NASA's Goddard Space Flight Center, has found that polar mesospheric clouds are forming more frequently and becoming brighter. He has been observing the clouds in data from Solar Backscatter Ultraviolet instruments that have been flown on satellites since 1978. The graph above shows how the brightness of the clouds has changed in the Northern Hemisphere. For reasons no one fully understands, the brightness wiggles up and down in step with solar activity, with fewer clouds forming when the Sun is most active. The biggest variability is in the far north. Underlying the changes caused by the Sun, however, is a trend toward brighter clouds. The upward trend in brightness, says DeLand, reveals subtle changes in the atmosphere that may be linked to greenhouse gases.

Polar mesospheric clouds are extremely sensitive to changes in atmospheric water vapor and temperature. The clouds form only when temperatures drop below -130 degrees Celsius (-200 Fahrenheit), when the scant amount of water high in the atmosphere freezes into ice clouds. This happens most often in far northern and southern latitudes (above 50 degrees) in the summer when, counter-intuitively, the mesosphere is coldest.

Changes in temperature or humidity in the mesosphere make the clouds brighter and more frequent. Colder temperatures allow more water to freeze, while an increase in water vapor allows more ice clouds to form. Increased water vapor also leads to the formation of larger ice particles that reflect more light.

The fact that polar mesospheric clouds are getting brighter suggests that the mesosphere is getting colder and more humid, says DeLand. Increasing greenhouse gases in the atmosphere could account for both phenomena. In the mesosphere, carbon dioxide radiates heat into space, causing cooling. More methane, on the other hand, puts more water vapor into the atmosphere because sunlight breaks methane into water molecules at high altitudes.

So far, it’s not clear which factor—water vapor or cooling—is causing polar mesospheric clouds to change. It’s likely that both are contributing, says DeLand, but the question is the focus of current research.

Image Credit & Copyright: Jan Erik Paulsen
Explanation from: http://earthobservatory.nasa.gov/IOTD/view.php?id=48892

Geminid Meteors over Paranal

Paranal, Chile

December 14, 2012

Image Credit & Copyright: Stéphane Guisard

Sunset seen from the International Space Station

This spectacular image of sunset on the Indian Ocean was taken by astronauts aboard the International Space Station (ISS). The image presents an edge-on, or limb view, of the Earth’s atmosphere as seen from orbit. The Earth’s curvature is visible along the horizon line, or limb, that extends across the image from center left to lower right. Above the darkened surface of the Earth, a brilliant sequence of colors roughly denotes several layers of the atmosphere.

Deep oranges and yellows appear in the troposphere, which extends from the Earth’s surface to 6–20 km high. This layer contains over 80 percent of the mass of the atmosphere and almost all of the water vapor, clouds, and precipitation. Several dark cloud layers are visible within this layer. Variations in the colors are due mainly to varying concentrations of either clouds or aerosols (airborne particles or droplets).

The pink to white region above the clouds appears to be the lower stratosphere; this atmospheric layer generally has few or no clouds, and it extends up to approximately 50 kilometers above the Earth’s surface. Above the stratosphere, blue layers likely mark the transition between the middle and upper atmosphere as it gradually fades into the blackness of outer space.

The ISS was located over the southern Indian Ocean when this picture was taken, with the astronaut looking towards the west. Astronauts aboard the ISS see 16 sunrises and sunsets per day due to their high orbital velocity (greater than 28,000 km per hour). The multiple chances for photography are fortunate because at that speed, each sunrise or sunset only lasts a few seconds!

Image Credit: NASA
Explanation from: http://earthobservatory.nasa.gov/IOTD/view.php?id=44267

Cloudy Night of the Northern Lights

On September 26, 2011, a large solar Coronal Mass Ejection smacked into planet Earth's magnetosphere producing a severe geomagnetic storm and wide spread auroras. Captured here near local midnight from Kvaløya island outside Tromsø in northern Norway, the intense auroral glow was framed by parting rain clouds. Tinted orange, the clouds are also in silhouette as the tops of the colorful shimmering curtains of northern lights extend well over 100 kilometers above the ground. Though the auroral rays are parallel, perspective makes them appear to radiate from a vanishing point at the zenith. Near the bottom of the scene, an even more distant Pleiades star cluster and bright planet Jupiter shine on this cloudy northern night.

Image Credit & Copyright: Fredrick Broms
Explanation from: http://apod.nasa.gov/apod/ap110930.html

Milky Way Galaxy over Quiver Tree Forest

Quiver Tree Forest, Namibia

June 2, 2012

Images Credit & Copyright: Florian Breuer