Astronomy in English: June 2008

Monday, 30 June 2008

A Sky Filled with Leonids

In the early morning hours of November 19, amateur Chen Huang-Ming caught a sky filled with astronomical wonders. With his fisheye camera set up on Ho-Huan Mountain in Taiwan for a half-hour exposure, he started the above image a local time of 2:33 am. First, the many famous stars and nebulas captured are too numerous to count. Planets Jupiter and Saturn are visible, while the plane of our Milky Way Galaxy sweeps diagonally across the image. What makes this image most spectacular, however, are the over 100 bright meteors visible from the 2001 Leonids Meteor Shower. The meteor shower is caused by the Earth plowing through a stream of sand-sized ice particles shed years ago by Comet Tempel-Tuttle. Note that the meteors can all be tracked back to a radiant in the constellation Leo, the direction from which the particles orbit the Sun.

AE Aurigae The Flaming Star

Is star AE Aurigae on fire? Although surrounded by what may look like smoke, the object known as the "flaming star" creates energy primarily by nuclear fusion, like other stars. Fire, typically defined as the rapid molecular acquisition of oxygen, happens only when sufficient oxygen is present and is not important in such high-energy, low-oxygen environments such as stars. The material that appears as smoke is mostly interstellar hydrogen, but does contain smoke-like dark filaments of carbon-rich dust grains. The AE Aurigae region was imaged by the KPNO 0.9-meter telescope and is shown above in false but representative colors. The star AE Aurigae itself is very bright, young, blue, and known as a runaway star since it appears to have been ejected from the Orion Nebula region about 2.7 million years ago.

Dueling Auroras

Will it be curtains for one of these auroras? A quick inspection indicates that it is curtains for both, as the designation curtains" well categorizes the type of aurora pattern pictured. Another (informal) type is the corona.The above auroras resulted from outbursts of ionic particles from the Sun during the last week of September. A polarity change in the solar magnetic field at the Earth then triggered auroras over the next few days.The above picture was taken on October 3 as fleeting space radiation pelted the Earth's atmosphere high above the Yukon in Canada.

Rumors of a Strange Universe

Three years ago results were first presented indicating that most of the energy in our universe is not in stars or galaxies but is tied to space itself. In the language of cosmologists, a large cosmological constant is directly implied by new distant supernovae observations. Suggestions of a cosmological constant (lambda) are not new -- they have existed since the advent of modern relativistic cosmology. Such claims are not usually popular with astronomers, though, because lambda is so unlike known universe components, because lambda's value appears limited by other observations, and because less-strange cosmologies without lambda have previously done well in explaining the data. What is noteworthy here is the seemingly direct and reliable method of the observations and the good reputations of the scientists conducting the investigations. Over the past three years, two independent teams of astronomers have continued to accumulate data that appears to confirm the unsettling result. The above picture of a supernova that occurred in 1994 on the outskirts of a spiral galaxy was taken by one of these collaborations. Still, extraordinary claims require extraordinary evidence, and so cosmologists the world over continue to await more data and confirmation by independent methods.

Neptune's Great Dark Spot Gone But Not Forgotten

When NASA's Voyager 2 spacecraft flew bydistant Neptune in August of 1989 astronomerswere shocked.Since Neptune receives only 3 percentthe sunlight Jupiter does, theyexpected to find a dormant, dark, frigid planet.Instead, the Voyager images revealedevidence of a dynamic and turbulent world.One of the most spectacular discoveries was of the Great Dark Spot, shown here in close-up.Surprisingly, it wascomparable in size and at the same relative southern latitude as Jupiter'sGreat Red Spot, appearing to be asimilar rotating storm system.Winds near the spot were measured up to1500 miles per hour, the strongest recorded on any planet.The Voyager data also revealed that the GreatDark Spot varied significantly in size during the brief flyby.When the HubbleSpace Telescope viewed the planet in 1994, the spot hadvanished -- only to be replaced by another darkspot in the planet's northern hemisphere!

Meteor Storm Sights and Sounds

This dramatic four-frame animation shows a fireball meteor and itsdeveloping persistent "smoke" train, recorded two weeks ago i skies nearSalvador, Brazil.Indeed similar sights are astonishingly familiar world-wide towitnesses of this November's fireball-ric Leonid meteor storm.A few skygazers even discoveredthat some bright Leonid fireballs made faint, gentle,hissing sounds(!), a surprising effect only recentlyappreciated and understood.Accounts of fireballmeteors making noise have long bee viewedwith skepticism, particularly because sounds werereportedly heard just as the meteor was seen overhead.But light travels much faster than sound so, like delaye thunder froma distant lightning stroke, ameteor produced sound should onlybe heard long after th meteor streak was seen Asound explanation supported b laboratorytests is that turbulen plasma created by the meteor's passagegenerates very low frequency radio waves Travelingat light speed the radio waves reach the groundsimultaneously with visible light where they are strong enough to induceoscillating current andaudible vibrations in common objectslike grass, leaves,wire-frame glasses, and perhaps even dry, frizzy hair.

Coronal Inflow

The active Sun has thrown a lot our way lately, includin storms of particlesstreaming outward in the solar wind an clouds of plasmawhich triggered awesome auroral displays.Still, a growing body of intriguing observationsfrom the LASCO instrument on board th space-basedSOlar and Heliospheric Observatory SOHO)indicates material also flows back toward the Sun, starting fromover 2 million kilometers above it visible surface.Relatively hard to detect against the outflowin solarcorona, a dark inflowing cloud's relative motion is trackedabove in two highly processed images recorded an hour apart.The solar surface, graphically shown by the yellowquarter circle at the lower right,is blocked from view by a smoot occulting disk.Fighting against solarwind outflow of about 120 kilometers persecond the cloud seems to be moving inward at 50-100 kilometers persecond.Occasionall appearing asoften as once per hour,the clouds, seem to be dragged in by collapsin magnetic field loops rather than gravity alone.Researchers are no workingto relate this surprising inflow to thesolar wind and magneti environmentof the Sun.

Extra Solar Planetary Atmosphere Detected

By directly detecting the atmosphere of a planet outside our Solar System, humanity has taken another small step toward finding extraterrestrial life.The unexpected detection by David Charbonneau Caltech) and associates came from Hubble Space Telescope observations of Sun-like star HD 209458. As an orbiting planet crossed between that star and the Earth, sodium in the planet's atmosphere absorbed starlight at very specific colors. The planet, originally discovered two years ago, has about 70 percent the mass of Jupiter but orbits very close in. A long-term goal of this type of research is the detection of planetary biomarkers that would indicate life, such as oxygen, water, or methane.

Ancient Layered Rocks on Mars

Is this a picture of Mars or Earth? Oddly enough, it is a picture of Mars. What may appear to some as a terrestrial coastline is in fact a formation of ancient layered rocks and wind-blown sand on Mars. The above-pictured region spans about three kilometers in Schiaparelli Crater. What created the layers of sediment is still a topic of research. Viable hypotheses include ancient epochs of deposit either from running water or wind-blown sand. Winds and sandstorms have smoothed and eroded the structures more recently. The "water" that appears near the bottom is actually dark colored sand. The image was taken with the Mars Global Surveyor spacecraft that has now returned over 100,000 images. News: APOD is now also available in Spanish.

Leonids from the Road

Sometimes you just have to stop and watch the meteors. In the early morning hours of November 18, a band of eleven people searched for a flat and cloudless site to see the 2001 Leonids Meteor Shower. Starting in central Iowa, weather satellite images indicated that southern Minnesota might be their best chance, and so off they drove. Although they couldn't shake off all of the clouds, they found a dark gravel road, pulled off, and settled in for the rare celestial light show. "By about 4 am, we were visually counting 1000 per hour. After that they started to increase dramatically." The photographer was just a little too late to catch a really bright fireball, but did catch several other bright Leonid meteors above one of the cars in the convoy. The exposure lasted a few minutes. News: APOD is now also available in Spanish.

M16 Stars from Eagle's EGGs

Newborn stars are forming in the Eagle Nebula. This image, taken with the Hubble Space Telescope in 1995, shows evaporating gaseous globules (EGGs) emerging from pillars of molecular hydrogen gas and dust. The giant pillars are light years in length and are so dense that interior gas contracts gravitationally to form stars. At each pillars' end, the intense radiation of bright young stars causes low density material to boil away, leaving stellar nurseries of dense EGGs exposed. The Eagle Nebula, associated with the open star cluster M16, lies about 7000 light years away.

Mariner's Mercury

Mercury, the closest planet to the Sun, remain the most mysterious of theSolar System's inner planets.Hiding in the Sun's glare it i adifficult target for Earth bound observers.The only spacecraft t explore Mercuryclose-up was Mariner 10 whichexecuted thre flybys of Mercuryin 1974 and 1975, surveying approximately 45percent of its surface Mariner10 deftly manuevered tophotograph part of the sunlithemisphere during each approach, passed behind the planet,and continued to image the sun-facing side as the spacecraft receded.Its highest resolutio photographs recorded featuresapproximately a mile across.A reprocessin of theMariner 10 data has resulted in this dramatic mosaic. Like the Earth's Moon, Mercury's surfaceshows the scars of impact cratering -the smooth vertical band and patches visible above represent regionswhere no image information is available.

Counting Falling Stardust

In the clear, dark and moonless predawn hours o November 18,Greenbelt, Maryland's local baseball field was packed.The crowd stared skyward and occasionally conversed in hushedand reverent tones."How man didyou count?" a man asked.Some had long since lost track ... but others were keeping score countinghundreds o Leonidmeteors in a short hour's worth of skygazing.Farther to the west, near Florence, Arizona recreationalastronomers also gathered to enjo thecelestial show.Taken fro thatlocation, this single, 10 minute, wide-angle exposur captured a dozen or so Leonid meteors.The shooting stars are clearly seen to b streaming from the shower' radiant point in the constellation Leo.

Fireball, Smoke Trail, Meteor Storm

Returning from orbit,space shuttles enter the atmosphere atabout 8 kilometers per second as friction heats their protectiveceramic tiles to over 1,400 degrees Celsius.By contrast, the bits of comet dust which became th Leonid meteorsseen on November 18, were moving at 70 kilometers per second,completely vaporizing at altitudes of around 100 kilometers In thissingle 5 minute time exposure, three Leoni meteors areshootin through skies above Spruce Knob,West Virginia, USA Background starsare near the constellation Orion.The brightest meteor, afireball, dramatically changes colors along itspath and leaves a smoke persistant trail driftingin high-altitude winds.From that extremely dark site, at an elevation of 1,200 meters astrophotographerJerry Lodriguss reports, "We observed a zenithalhourly rate] of about 3,600 at 10:30 UT andvery high rates from 9:30 UT until well into the startof astronomical twilight at 10:50 UT. It was quite spectacular storm,with bolides going off like flashbulbs,green and red fireballs and other fainter Leonids in all parts ofthe sky."

The Galactic Ring of NGC 6782

Do spiral galaxies look the same in every color? NGC 6782 demonstrates colorfully that they do not. In visible light, NGC 6782 appears to be a normal spiral galaxy with a bright bar across its center. In ultraviolet light, however, the central region blossoms into a spectacular and complex structure highlighted by a circumnuclear ring, as shown in the above representative color Hubble Space Telescope image. Many of the young stars that formed in a recent burst of star formation emit the ultraviolet light. Astronomers are studying possible relationships between the central bar and the ring. Light we see today from NGC 6782 left about 180 million years ago, while dinosaurs roamed the Earth. The galaxy spans about 80,000 light-years and can be seen with a telescope toward the constellation of Pavo.

A Leonids Star Field

As meteor after meteor streaked across a moonless sky, photographers across the world snapped pictures of the 2001 Leonids Meteor Shower. Many recognized this as the best meteor shower they had ever seen. In fact, the 2001 Leonids was the most active meteor shower since the mid-1960s. The above photo captures three Leonid meteors crossing a photogenic star-field. On the far right is the Pleiades star cluster. The brightest meteor crosses right in front of the Hyades star cluster, situated below the image center. Just left of center is the bright plane Saturn, and the bright star belowSaturn is Aldebaran. The ten-minute exposure was taken near Victoria, British Columbia, Canada at 2:45 am PST on 2001 November 18.

A 2001 Leonids Meteor Shower Fireball

The 2001 Leonids Meteor Shower gave quite a show to many parts of the world yesterday during the early morning hours. Many sleepy observers venturing into their own backyards were treated to several bright meteors per minute streaking across the sky. This rate made the 2001 Leonids the most active meteor shower in over three decades. Pictured above is a bright Leonid fireball that briefly lit up Hawaii yesterday morning. A CONCAM nighttime all-sky monitor on Mauna Kea, a dormant volcano, caught the bright meteor, seen as the very bright streak across the lower part of the fisheye image. The meteor track crossed the Galactic plane (the faint glow that runs from the lower left to upper right), passed below the planet Jupiter, and through the constellation Orion. CONCAMs in Hawaii, Arizona, and California all recorded numerous bright meteors during this year's Leonids.

A Leonid Meteor Explodes

Last night and tonight, a lucky few may see a meteor explode. As our Earth passes unusually close to debris expelled from Comet Tempel-Tuttle, many sand-sized particles from this comet areentering and burning up in the Earth's atmosphere. This yearl phenomenon is known as the Leonids Meteor Shower, but the location the Earth passes through this year holds promise to provide relatively high activity. In particular, the 1998 Leonids was noteworthy for its many bright meteors. In the above slow-loading sequence, a 1998 Leonid was caught exploding over Los Alamos, New Mexico. In the last one-minute exposure, another Leonid streaks past.

Catching Falling Stardust

This carrot-shaped track is actually little more than 5 hundredthsof an inch long.It is the trail of a meteroid through the high-tec substance aerogelexposed to space by the shuttle launche EURECA(European Recoverable Carrier) spacecraft Like those i the ongoing Leonid meteor shower, thismeteoroid is about a thousandth of an inch in diameter.It is visible where it came to rest, justbeyond the tip of the carrot at the far right.Chemical analyses o interplanetary dust particles similarto this one suggest that some of them may b bitsof comets and thus represent samples of material fro theearly stages of the formation of the Solar System.

Leonid Watching

Will the Leonids storm this year?The annual Leonid meteor shower should pea this weekend and somepredictions suggest that "storm" rates of a thousand or more meteorsper hour are possible for observers located in eastern Northand Central Americaduring the early morning hours of Sunday, November 18.Similar high rates are also anticipated for the western Pacific regionon the morning of November 19th.In any event, th 2001 Leonidshower should be dramatic an easy to watch, as were th Leonids of recent years.From top left to bottom right above are spectacula examples ofbright fireball meteors from the 1998 Leonid shower as recorded b V. Winter and J. Dudley Lorenzo Lovato, an Wally Pacholka.A 1998 image from the Puckett Observatory at lower leftfeatures the source of th debris stream which suppliesthe Leonid meteors comet Tempel-Tuttle.

Recycling Columbia

Twenty years ago this week, th Space Shuttle Columbia becamethe first reusable spaceship Its second trip to low Earth orbit and back again beganon November 12, 1981, following it maiden voyage by only seven months.Seen above Columbia, 56 meters (184 feet) long with a24 meter (78 foot) wingspan, is launched mated to anexternal fuel tank and two solid rocket boosters producingdramatic exhaust plumes.The solid rocket boosters,one on each side of the external tank, provide most of the thrust inthe first 2 minutes after launch and are then jettisoned forlater recovery.Supplying the main shuttle engines during liftoff, th external fuel tank separates after about 8 minutes.The largest shuttle element not recycled for a futureflight, the external tank falls backtoward Earth breaking up and descending into a remote ocean area.Still the oldest operating shuttle, Columbia i pictured herein June of 1992 rocketing toward a cloud bank o its twelfth flight.Officially designated OV-102, Columbia i fittingly named after the 18thcentury sailing vessel which became the firs Americanship to circumnavigate planet Earth.

Auroras Over Both Earth Poles

Auroras in the north and south can be nearly mirror images of each other. Such mirroring had been suspected for centuries but dramatically confirmed only last month by detailed images from NASA's orbiting Polar spacecraft. Pictured above, a time-lapse movie shows simultaneous changes in aurora borealis, at the top, and aurora australis, at the bottom. A cloud of electrons and ions moving out from the Sun on October 22 created the auroras. The solar explosion that released the particles occurred about three days earlier.

A Gravity Map of Earth

Is gravity the same over the surface of the Earth? No -- it turns out that in some places you will feel slightly heavier than others. The above relief map shows in exaggerated highs and lows where the gravitational field of Earth is relatively strong and weak. A low spot can be seen just off the coast of India, while a relative high occurs in the South Pacific Ocean. The cause of these irregularities is unknown since present surface features do not appear dominant. Scientists hypothesize that factors that are more important lay in deep underground structures and may be related to the Earth's appearance in the distant past. To better map Earth's gravity and hence better understand its interior and past, NASA plans to launch the Gravity Recovery and Climate (GRACE) satellite in February.

Is Mystery Object an Orphan Afterglow

What is that unusual object? Astronomers can identify most objects that are imaged on the sky, but not all. Pictured above is one that currently defies classification. Attributes of the object include that it has unusual colors, appears to be fading as months go by, and appears to be associated with a distant galaxy. Its discoverers hold hope that they have uncovered the first known orphan afterglow, an explosion that would have been classified as a gamma-ray burst if the gamma-rays were beamed in our direction. Orphan afterglows, if they exist, could have unparalleled brightness, and hence be visible so far away that they yield key information about the early years of our universe.A bit of caution might be merited, however, as the last well-publicized mystery object turned out not to be a new member of the astronomical zoo, but rather an unusual type of quasar. Follow-up observations and analysis over the next year may find more objects like this and/or solve this mystery.

An Annotated Leonid

The 1998 Leonids Meteor Shower was one of the most photographed meteor events in history. Patient observers saw bright meteors streak across dark skies every few minutes, frequently leaving fading trails stretching across the sky. High above the Anza-Borrego Desert, a meteor was photographed streaking up from the radiant constellation of the Leonids: Leo. This meteor train covered over 40 degrees, and changed colors from green to red. The intensity of the Leonid Meteor Shower in 2001 is uncertain but may approach one per second for somelocations on November 18.

Lunar Dust and Duct Tape

Why is the Moon dusty?On Earth, rocks are weathered by wind and water, creating soil and sand.On the Moon, the long history o micrometeorite bombardmenthas blasted away at the rocky surface creating a layer of powder lunar soil or regolith.This lunar regolith could be scientific an industrial bonanza.But for the Apollo astronauts an their equipment,the pervasive, fine, gritty dust was definitely a problem Onthe lunar surface in December 1972 Apollo 17 astronautsHarrison Schmitt and Eugene Cernan needed to repair one of theirlunar rover's fender in an effort to keep the"rooster tails" of dust away from themselves and their gear This picture reveals the wheel andfender of their dust covere rover along withthe ingenious application of spare maps,clamps, and a grey strip of "duct tape".

SOHO Comet 367 Sungrazer

The most prolific comet discovering instrumentin history rides aboard th sun-staringSOHO spacecraft, 1.5 million kilometers sunward of planet Earth.Of course, most of these SOHOcomets have bee sungrazers -like the one illustrated in the dramatic montage above.Three frames taken hours apart on October 23rd, showbright SOHO comet number 367plunging toward the fiery solar surface its tail streaming awayfrom the Sun located just beyond the left hand border.Each panel spans about one million kilometers a the distance o the Sun.From bottom to top, the comet's tail grows as the intensifyingsolar radiation heats the frozen comet material and increases theoutflow of gas and dust.Because of their orbits sungrazersare believed to belong to afamily of comets produced by the breakup of a single much largercomet.Coincidentally, this sungrazer wa discoveredshortly after solar active regionsblasted out clouds of energetic particles, like those thattriggered the recent spectacula auroralstorms.And like all SOH sungrazers so far,comet number 367 was not seen to survive its close solar encounter.

Under A Sunspot

At the Sun's surface, sunspots are known to be dark planet-sized regions ofintense magnetic fields.But what lies below?Using observations from th MichelsonDoppler Imager (MDI) instrument aboard the space-base SOHOobservatory, astronomers have derive thispremier picture of the flowof material just beneath visible sunspot.The MDI data indicate that immediatel underthe sunspot a strong inflowing current exists, shown aboveby the dark arrows.This converging undertowpulls near-surface material toward the spot and preventsthe concentrated magnetic fields from flying apart,like repelling poles o ironmagnets.Such a configuration appears to divert the normal flo of plasmabubbling up from the solar interior, creating self-sustainingsunspot.The MDI instrument can explore the properties of the solar interiorby detecting motions produced b sound wavesas they interact at the solar surface.

Sunday, 29 June 2008

A Sun Pillar in Red and Violet

Sometimes the unknown is beautiful. In 2000 February near Lake Tahoe, Nevada, two amateur photographers noticed an unusual red column of light rise mysteriously from a setting sun. During the next few minutes, they were able to capture the pillar and a photogenic sunset on film. Pictured above, the red column is seen above a serene Lake Tahoe and snow-capped mountains across fro Lake Tahoe-Nevada State Park. The mysterious column, they learned later, is a Sun Pillar, a phenomenon where sunlight reflects off of distant falling ice crystals.

In the Center of Spiral Galaxy M83

What's happening at the center of spiral galaxy M83? Just about everything, from the looks of it. M83, visible in the inset image on the upper left, is one of the closest spiral galaxies to our own Milky Way Galaxy and from a distance of 15 million light-years, appears to be relatively normal. Zooming in on M83's nucleus with the latest telescopes, however, shows the center to be an energetic and busy place. Visible in the above image from the Hubble Space Telescope are bright, newly formed stars and giant lanes of dark dust. An image with similar perspective from the Chandra X-ray Observatory shows the region is also rich in very hot gas and small bright sources. Observations with the large ground-based VLT telescopes show the very center likely has two separate nuclei.

Aurora Over Winnipeg

What's happening above that city? The city is Winnipeg, Canada, and the phenomenon is aurora. These past few months have been active ones for our Sun, producing several coronal mass ejections (CMEs) of particles that have swept past our Earth and caused many spectacular auroras. Specifically in this case, a CME that occurred on October 9 impacted the Earth on October 11 and 12, causing nearly 12 hours of auroras. The above-pictured aurora had to be very bright to be seen over the lights of Winnipeg, the city well below and in front of the cascading atmospheric airglow. Lights reflecting off of a slight haze cause an unrelated glow that emanates from some of the buildings.

Leonids from Leo

Is Leo leaking? Leo, the famous sky constellation visible on the left of the above all-sky photograph, appears to be the source of all the meteors seen in 1998's Leonids Meteor Shower. That Leonids point back to Leo is not a surprise - it is the reason that this November meteor shower is called the Leonids. Sand-sized debris expelled from Comet Tempel-Tuttle follows a well-defined orbit about our Sun, and the part of the orbit that approaches Earth is superposed in front of the constellation Leo. Therefore, when Earth crosses this orbit, the radiant point of falling debris appears in Leo. Over 150 meteorscan be seen in the above four-hour effort. The intensity of the Leonid Meteor Shower in 2001 is uncertain but may approach one per second for some locations on November 18.

Bright Stars, Dim Galaxy

These two clusters of bright, newly formed star surrounded bya glowing nebula lie 10 million light-years away in the dim,irregular galaxy cataloged as NGC 2366.The HubbleSpace Telescope image shows that the youngest cluster,the bottom one at about 2 million years old,is still surrounded by the gas and dust cloud it condensed from, whil powerful stellar winds from the starsin the older cluster at the top (4-5 million years old),have begun to clear away its central areas giving the entire nebulaan apparent inverted hook shape.Compared to the sun, the stars in these cluster are massive an short lived.The brightest one, near the tip of the hook, is a rare Luminous Blue Variablewith 30 to 60 times the mass of the sun - similar to the erruptiv Eta Carinae in our own Milky Way.Stars this massiv are extremely variable.A comparison with ground based images indicates that in threeyears this star's brightness increased by about 40 times making it currentlythe brightest star i this dim galaxy.

THEMIS of Mars

Not an ancient Greek goddess, THEMIS i modern acronese fo THermal EMission Imaging System.Above is this remarkable instrument' premier infrared image ofMars, from the newly orbitin Mars Odyssey spacecraft.Taken on October 30th, the sharp infrared picture covers the indicatedswath of the martian southern hemisphere and showssurface temperatures in false-colors ranging from red, a warm 0 degreesCelsius, to cool purple shades of -120 degrees C.The striking, cold circular feature i Mars' south polar ice cap.Composed of froze carbon dioxide, the ice cap is about 900 kilometers wid and shrinkingduring the onslaught of southern hemispher summer.Temperatures are also seen to drop as the bottom portionof the THEMIS image sweep beyondthe terminator or shadow line, into the martia night.A thin, light blue crescent along the upper edge of the planet is th martian atmosphere. The THEMIS image data was recorded a a test ofthe camera systemfrom an altitude of about 22,000 kilometers .

M87's Energetic Jet

Anenergetic jet from the core ofgiant elliptical galaxy M87 stretches outward for 5,000 light-years.This monstrous je appearsin the panels above to be a knotted and irregular structure, dectecte across the spectrum, fromx-ray to optical t radio wavelengths.In all these bands,the observed emission is likely created as high energyelectrons spiral along magnetic field lines, so calle synchrotron radiation.But what powers this cosmic blowtorch?Ultimately, the jet is thought to be produce as matter near the center of M87swirls toward a spinning, supermassive black hole.Strong electromagnetic forces are generated and eject materialaway fro the black hole alongthe axis of rotation in a narrow jet Galaxy M87is about 50 million light-years away and reigns asthe large central elliptical galaxy in th Virgocluster.

Halloween and the Ghost Head Nebula

Halloween's origin is ancient and astronomical. Since the fifth century BC, Halloween has been celebrated as a cross-quarter day, a day halfway between an equinox (equal day / equal night) and a solstice (minimum day / maximum night in the northern hemisphere). With our modern calendar, however, the real cross-quarter day will occur next week. Another cross-quarter day is Groundhog's Day Halloween'smodern celebration retains historic roots in dressing to scare away the spirits of the dead. A perhaps-fitting modern tribute to this ancient holiday is the above-pictured Ghost Head Nebula taken with the Hubble Space Telescope. Appearing similar to the icon of a fictional ghost, NGC 2080 is actually a star forming region in the Large Magellanic Cloud, a satellite galaxy of our own Milky Way Galaxy. The Ghost Head Nebula spans about 50 light-years and is shown in representative colors.

Anticrepuscular Rays Over Colorado

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. Pictured above 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. Pictured above is a particularly striking set of anticrepuscular rays photographed earlier this month from a moving car just outside of Boulder, Colorado, USA.

Spinning Black Holes and MCG 6 30 15

What makes the core of galaxy MCG-6-30-15 so bright? Some astronomers believe the answer is a massive spinning black hole. If so, this would be the first observational indication that it is possible to make a black hole act like a battery -- and tap into its rotational energy. MCG-6-30-15 is a distant galaxy that has recently been observed with the orbiting XMM-Newton satellite in X-ray light. These observations show the galaxy's nucleus not only to be very bright but also to show evidence that much of the light is climbing out of a deep gravitational well. A spinning black hole could explain both effects. A strong magnetic field could be the mediator transferring rotational energy from the black hole to the surrounding gas. Pictured above is an artist's illustration of a black hole surrounded by an accretion disk. For clarity, the illustration does not include distorting gravitational lens effects.

NGC 2346 A Butterfly-Shaped Planetary Nebula

It may look like a butterfly, but it's bigger than our Solar System. NGC 2346 is a planetary nebula made of gas and dust that has evolved into a familiar shape. At the heart of the bipolar planetary nebula is a pair of close stars orbiting each other once every sixteen days. The tale of how the butterfly blossomed probably began millions of years ago, when the stars were farther apart. The more massive star expanded to encompass its binary companion, causing the two to spiral closer and expel rings of gas. Later, bubbles of hot gas emerged as the core of the massive red giant star became uncovered. In billions of years, our Sun will become a red giant and emit a planetary nebula - but probably not in the shape of a butterfly, because the Sun has no binary star companion.

Sher 25 A Pending Supernova

No supernova has ever been predicted.These dramatic stellar explosions that destroy stars and disperse elements that compos people and planetsare not so well understood that astronomers can accurately predict when a star will explode - yet.Perhaps Sher25 will be the first.Sher 25, designated by the arrow, is a blu supergiant star located just outside the star cluster and emission nebul NGC 3603.Sher 25 lies in the center of an hourglass shaped nebula much like the one that surrounds the last bright supernova visible from Earth: SN1987a.Now the hourglass shaped rings around SN1987a were emitted before that blue supergiant exploded. Maybe Sher 25 has expelled these bipolar rings in a stepthat closely precedes a supernova. If so, Sher 25 may be withina few thousand years of its spectacular finale.

Elements in the Aftermath

Massive starsspend their brie lives furiously burning nuclear fuel Through fusionat extreme temperatures and densities surrounding thestellar core, nuclei of light element like Hydrogen and Helium are combined to heavie elements likeCarbon, Oxygen, etc. in a progression which ends with Iron.And so a supernova explosion,a massive star's inevitable and spectacular demise,blasts back into space debri enriched inheavier elements to be incorporated into other stars and planets (an people!).This detaile false-color x-ray imagefrom the orbiting ChandraObservatory shows such a hot, expanding stella debriscloud about 36 light-years across.Cataloged as G292.0+1.8, this young supernova remnantin the southern constellatio Centaurus resulted froma massive star which exploded an estimated 1,600 years ago.Bluish colors highlight filaments of the mulitmillion degree gaswhich are exceptionall rich in Oxygen, Neon, and Magnesium.Just below and left of center, a point like object in the Chandra imagesuggests tha theenriching supernova also produced a pulsar inits aftermath, a rotating neutron star remnant of the collapsed stellarcore.

Odyssey at Mars

After an interplanetaryjourney lasting 200 days, the Mars Odyssey spacecraf hasentered orbit around the Red Planet.This latest success is welcome as in the past, Mars has often seemed adifficult planet to visit Beginning with the firstSoviet attempts in 1960, around 30 missions havetried while only 10 or so have gone without serious mishap.Now tha Mars Odysseyhas arrived, its immediate future will involv aerobraking.Cautiously dipping into th martian atmosphere, the spacecraft willgradually adjust its present wide and elliptical 20-hourorbit to a circular 2-hour orbit only 400 kilometers above th planet's surface.Then, its instruments an cameras will focus on exploringthe climate and geologic histor of Mars, including th search for waterand evidence of life-sustainin environments.In the artist's conception above, the spacecraft with wing-like solar panelsis imagined firing its rocket engine fo Mars orbit insertion over terrain seenin natural and false-color.

The Matter of Galaxy Clusters

Situated over 2,000,000,000 two billion)light-years from Earth, galaxies in cluster Abell 2390 (top) andMS2137.3-2353 (bottom are seen in the right hand panels above,false-color images from th HubbleSpace Telescope.Corresponding panels on the left reveal each cluster' x-rayappearance in images from the Chandra X-ray Observatory.While the Hubble images record the cluster's star-filled galaxies,the x-ray images show no galaxies at all ... onlymulti-million degree hot intracluster ga which glows in high energy x-rays.But there lies a profound mystery.The total mass in the galaxies on the right, plus themass of the hot gas on the left, falls far short of providing enough gravityto confine the hot gas withi the galaxy clusters.In fact the best accounting to datecan only find 13 per cent (!)of the total matter necessary Gravitational lensarcs visible in the deep Hubble imagesalso indicate these clusters have much more mass than directly identifiablein the Chandra and Hubble data.Astronomers conclude that most of the cluster matter i dark matter,invisible even to the combined far-seeing eyes of these orbitin astrophysical observatories.What is thenature of this cosmic dark matter?

Emission and Reflection in NGC 6559

Bright gas and dark dust permeate the space between stars in a nebula known as NGC 6559. The gas, primarily hydrogen, is responsible for the diffuse red glow of the emission nebula. As energetic light from neighboring stars ionizes interstellar hydrogen, protons and electrons recombine to emit light of very specific colors, including the red hue observed. Small dust particles reflect blue starlight efficiently and so creates the blue reflection nebulosity seen near two of the bright stars. Dust also absorbs visible light, causing the dark clouds and filaments visible. NGC 6559 lies about 5000 light-years away toward the constellation of Sagittarius.

The First Rocket Launch from Cape Canaveral

A new chapter in space flight began on 1950 July with the launch of the first rocket from Cape Canaveral, Florida: the Bumper 2. Shown above, the Bumper 2 was an ambitious two-stage rocket program that topped a V-2 missile base with a WAC Corporal rocket. The upper stage was able to reach then-record altitudes of almost 400 kilometers, higher than even modern Space Shuttles fly today. Launched under the direction of the General Electric Company, the Bumper 2 was used primarily for testing rocket systems and for research on the upper atmosphere. Bumper 2 rockets carried small payloads that allowed them to measure attributes including air temperature and cosmic ray impacts. Seven years later, the Soviet Union launched Sputnik I and Sputnik II, the first satellites into Earth orbit. In response, in 1958, the US created NASA.

The Sombrero Galaxy from VLT

Why does the Sombrero Galaxy look like a hat? Reasons include the Sombrero's unusually large and extended central bulge of stars, and dark prominent dust lanes that appear in a disk that we see nearly edge-on. Billions of old stars cause the diffuse glow of the extended central bulge. Close inspection of the bulge in the above photograph shows many points of light that are actually globular clusters.M104's spectacular dust rings harbor many younger and brighter stars, and show intricate details astronomers don't yet fully understand. The very center of the Sombrero glows across the electromagnetic spectrum, and is thought to house a large black hole. Fifty million-year-old light from the Sombrero Galaxy can be seen with a small telescope towards the constellation of Virgo.

The Radio Sky Tuned to 408MHz

Tune your radio telescope to 408MHz(408 million cycles per second) and check out the Radio Sky!You should find that frequency on you dial somewhere betweenUS broadcast television channels 13 and 14.In the 1970s large dish antennas atthree radio observatories, Jodrell Bank MPIfR, an Parkes Observatory,were used to do just that the data were combined to map the entire sky.Near this frequency,cosmic radio waves are generated by high energy electrons spiralingalong magnetic fields.In the resulting false color image, the galactic planeruns horizontally through the center, but n stars are visible.Instead, many of the bright sources near the planeare distant pulsars, star forming regions,and supernova remnants, while the gran looping structuresare pieces o bubbles blown by local stellar activity.External galaxies lik Centaurus A, located above the plane to theright of center, an the LMC (below and right)also shine in the Radio Sky.

Saturday, 28 June 2008

X-Ray Stars and Winds in the Rosette Nebula

This mosaic of x-ray imagescuts a swath across the photogenicRosette Nebula, a stellar nursery 5,000 light-years from Earthin the constellation Monoceros theUnicorn.Constructed from data recorded by the orbitin Chandra X-ray Observatory,the mosaic spans less than 100 light-years and is colorcoded to show low energies in red and high energy x-rays in blue.At the upper right is the young star cluste NGC 2244, central tothe Rosette Nebula itself.The hot outer layers of the massive stars are seen to be copioussources of x-rays, but a diffuse x-ray glowalso pervades this cluster of newborn stars.Since these stars are so young (less than few million years old!) the diffusex-ray emission is thought to be powered by energetic collidingstellar winds ratherthan remnants of supernovae explosions,a final act in th life cycleof a massive star.Moving away from the center, south and east across the nebula(upper right to lower left),the hot, blustery environment gives way todense molecular gas, absorbing low energy x-rayswhile revealing the penetrating high energy x-rays from embedded stars.

Pluto New Horizons

Pluto'shorizon spans the foreground in this artist's vision,gazing sunward across that distant an not yet explored world.Titled New Horizons, the painting als depicts Pluto'scompanion, Charon, as a darkened, ghostly apparition witha luminou crescentagainst a starry background.Beyon Charon,the diminished Sun is immersed ina flattened cloud of zodiacal dust.Here, Pluto's ruddy colors are based on existin astronomicalobservations while imagined bu scientifically tenable detailsprovided by the artist include high atmospheric cirrus anddark plumes from surface vents, in analogy to Neptune's large moo Tritonexplored by th Voyager2 spacecraft in 1989.Craters suggest bombardment b KuiperBelt objects, a newly understoo population ofouter solar system bodies likel related to th Pluto-Charon system.NASA is now considering a future robotic reconnaissanc missionto Pluto-Charon and the Kuiper Belt which could reach the distantworlds late in the next decade.

Mars Engulfed

For months now Marshas been engulfed by a great dust storm, the biggestseen raging across th Red Planet i decades.As a result, these two Hubble Space Telescop stormwatch images from late June andearly September offer dramatically contrasting view of the martian surface.At left, the onset of smaller "seed" storms can be seen nearthe Hellas basin(lower right edge of Mars) and th northern polar cap.A similar surface view at right, taken over two months later,shows the fully developed extent of the obscuring global dust storm.The storm is reported to be waning, but planet-wide effects such as thewarming of the uppe martianatmosphere and cooling of the surface arestill being monitored daily b instruments on board the Mars GlobalSurveyor spacecraft.The present condition of the martian atmosphere i alsoimportant to the aerobraking MarsOdyssey spacecraft, scheduled to arriveat the Red Planet next week.

A Newly Active Volcano On Jupiters Io

Would a volcano plume discovered in January above Jupiter's Moon Io still be active months later? To answer this question, the robot spacecraft Galileo currently in orbit around Jupiter was maneuvered to image the plume site during its recent flyby of Io in August. What was found was the highest volcano plume yet discovered -- but above a completely different and previously undocumented volcano! The original plume, above the Tvashtar Catena volcanic area, was not even visible. A picture taken in January of the area surrounding the Tvashtar Catena eruption is shown above in enhanced color, with a new picture taken in August shown in the inset. Careful inspection of the two images will show a newly prominent dark volcano surrounded by a light-colored ring visible only in the smaller, more recent image.

The Earth and Moon Planetary System

How similar in size are the Earth and the Moon? A dramatic visual answer to this question is found by combining photographs taken by the Mariner 10 spacecraft that headed out toward Venus and Mercury in 1973. The Moon can be seen to have a diameter over one quarter that of Earth, relatively large compared to its planetary companion. In our Solar System, only Pluto and Charon are closer together in size. Striking features of the Earth visible to the passing spacecraft include blue oceans and white clouds, showing the Earth to be truly a water world.

Galileo Demonstrates the Telescope

Galileo Galilei made a good discovery great. Upon hearing at age 40 that Dutch optician had invented a glass that made distant objects appearlarger, Galileo crafted his own telescope and turned it toward the sky Galileo quickly discovered that our Moon had craters, that Jupiter had its own moons, that the Sun has spots, and that Venus has phases like our Moon Galileo, who lived from 1564 to 1642, made many more discoveries. Galileoclaimed that his observations only made sense if all the planets revolvedaround the Sun, as championed by Aristarchus and Copernicus, not the Earth,as was commonly believed then. The powerful Inquisition mad Galileo publicly recant this conclusion, but today we know he was correct.

A Portrait of Saturn from Titan

This artistic portrait of Saturn depicts howit might look from Titan, Saturn's largest moon.In the foreground sits ESA' Huygens probe, which will be released by NASA's Cassinispacecraft and parachute to Titan's surface. Cassini willreach Saturn in 2004 and release the Huygens probe later that year. Titan is one of only two moons in the Solar System to have an atmosphere.It has been suggested Titan might have gasoline-like lakesand an atmospheri chemistrylike that found on early Earth.The Cassini spacecraft was launched in October 1997and has now traveled beyond Jupiter.

Space Station and Space Shuttle Backyard View

Knowing when and whereto look, many enthusiastic sky gazers havebeen able to spot the International Space Station (ISS) asa bright star streakingthrough the twilight.But with a digital camera and a small telescope, recognizabl imagesare possible too.Astronomer Ricardo Borb offers this example of theSpace Shuttl Discovery docked wit the ISS, recorded this August fromhis backyard in Ottawa, Canada.Operating a digital video camera on an 8 inch reflecting telescope,Borba tracked the Earth-orbiting pair by hand.Unwanted telescope motion and atmospheri blurring caused most of thevideo frames to be indistinct, still the singlebest frame (left) from his video sequence is amazingly sharp.For comparison, he constructed a computer generatedimage (right) showing the approximate orientation of the Shuttle/ISS dockingconfiguration based o virtual3D models availabl on the web.

VDB 142 in Cepheus

A gorgeous collectionof dust and gas nebulae in th NorthernMilky Way graces the high and far off constellation of Cepheus.With colorsbased on astronomical filters, this close up of the regionhighlights stars embedded i curiously shaped cosmic clouds.Near the central faint (9th magnitude) star in the image,dust clouds reflect the starlight creating abluish reflection nebula cataloge in 1966as VDB 142.The area's bright reddish emission nebulaeindicate the presence ofclouds of atomic hydrogen gas.Stripped of electrons by invisible ultraviole light, the hydrogenatoms emit their characteristic visible re light a electrons andatoms recombine.Sweptback clouds of obscuring dust dark nebulae,are silhouetted against the bright background.Representing the stuff stars are made of, al thesenebulae lie withinthe large young star cluster comple IC 1396,3,000 light years from Earth.

The Center of Globular Cluster Omega Centauri

What is left over after stars collide? To help answer this question, astronomers have been studying the center of the most massive ball of stars in our Milky Way Galaxy. In the center of globular cluster Omega Centauri, stars are packed in 10,000 times more densely than near our Sun. Pictured above, the Hubble Space Telescope has resolved the very center of Omega Centauri into individual stars. Visible are many faint yellow-white stars that are smaller than our Sun, several yellow-orange stars that are Red Giants, and an occasiona blue star. When two stars collide they likely either combine to form one more massive star, or they stick, forming a new binary star system. Close binary stars interact, sometimes emitting ultraviolet or X-ray light when gas falls from one star onto the surface of a compact companion such as a white dwarf or neutron star. Two such binaries have now been located in Omega Centauri's center. The star cluster lies about 15,000 light-years away and is visible toward the constellation of Centaurus.

The Past of Asteroid Eros

How did large rocks come to be scattered on the surface of asteroid Eros? Eros stands out not only because of its proximity to Earth but alsobecause it was visited recently by NASA's NEAR-Shoemaker spacecraft. After arriving at Eros in 2000 February, the robot probe was maneuvered to a controlled landing earlier this year. Although NEAR-Shoemaker is no longer active, scientists are still poring over the images and data, finding new mysteries, and drawing new hypotheses about the ancient tumbling space mountain.For example, analyzing the locations of rocks has led to the hypothesis that many of them originated in a single large collision that occurred possibly about a billion years ago. Still unknown, however, includes why Eros has unusual ponds of blue dust.

A Yukon Aurora

Last week was another good week for auroras. The story began about two weeks ago when two large Coronal Mass Ejections exploded off the Sun. Waves of elementary particles and ions swept out past the Earth on September 28 and 29, causing many auroras. A week ago, a flapping sheet that divides north and south regions of the Sun's magnetic field passed the Earth, again causing auroras. Pictured above is a particularly good image of one of the October 1 northern lights. Taken in Canada's Yukon, the city lights of Whitehorse are seen below dark clouds and a twisting green aurora.

Abell 2218 A Galaxy Cluster Lens

Gravity can bend light, allowing huge clusters of galaxies to act as telescopes. Almost all of the bright objects in this released Hubble Space Telescope image are galaxies in the cluster known as Abell 2218. The cluster is so massive and so compact that its gravity bends and focuses the light from galaxies that lie behind it. As a result, multiple images of these background galaxies are distorted into long faint arcs - a simple lensing effect analogous to viewing distant streetlamps through a glass of wine. The cluster of galaxies Abell 2218 is itself about three billion light-years away in the northern constellation Draco.The power of this massive cluster telescope has recently allowed astronomers to detect a galaxy at redshift 5.58, the most distant galaxy yet measured. This young, still-maturing galaxy is faintly visible to the lower right of the cluster core.

Hen 1357 New Born Nebula

ThisHubble Space Telescope snapshot shows Hen-1357,the youngest known planetary nebula.Graceful, gentle curves and symmetr suggestits popular name TheStingray Nebula.Observations in the 1970s detected no nebular material, butthis image from March 1996 clearly shows the Stingray'semerging bubbles and rings of shocked and ionized gas.The gas is energized by the hot central star as it nears theend of its life, evolving toward final white dwarf phase.The image also shows a companion star (at about 10 o'clock) withinthe nebula.Astronomers suspect that such companionsaccount fo thecomplex shapes and rings ofthis and many other planetary nebulae.This cosmic infant is about 130 times the size of our own solar systemand growing.It is 18,000 light-years distant, in th southern constellation Ara.

A Flock of Stars

Only a few stars can b found within ten light-years of our lonely Sun situated nearan outer spiral arm of the Milky Way galaxy.But i the Sun were found withinone of our galaxy' starclusters, thousands of stars might occupy a similar space Whatwould the night sky look like in such a densely packed stellarneighborhood?When Roger Hopkins took this picture at th MontezumaNational Wildlife Refugein the Finger Lakes region of western New York, USA, he wasstruck by this same notion.Appropriately, he had photographe a flockof starlings against thebackdrop of a serene sunset.He then manipulated the image so that the blackbird silhouettes were changed to white The finalpicture dramatically suggests thetantalizing spectacle of approaching night in crowde skies above clusterstar world.

M74 The Perfect Spiral

If not perfect, then thi spiralgalaxy is at least one of the most photogenic.An island universeof about 100 billion stars,30 million light-years away toward th constellation Pisces,NGC 628 or M74 presents a gorgeou face-on viewto earthbound astronomers Classifiedas an Sc galaxy, the grand designof M74's graceful spiralarms traced by bright bluestar clusters and dar cosmic dust lanes,is similar in many respects to our own home galaxy, th Milky Way.Recorded with a 28 millio pixeldetector array, this impressiv image celebrates first light forthe Gemini Multi-Object Spectrograph GMOS), a state-of-the-art instrumentnow operational at the 8-mete Gemini North telescope.The Gemini North Observatory gazes into the skies abov Mauna Kea,Hawaii, USA, while its twin observatory Gemini South,is scheduled to begin operations later this year fromCerro Pachn in central Chile.

The Planetary Nebula Show

What do the Owl, the Cat's Eye, the Ghost of Jupiter, and Saturnhave in common?They're al planetary nebulaeof course(!), glowing gaseousshrouds shed by dying sun-like star asthey run out of nuclear fuel.Beautiful t look at,the symmetric planet-likeshapes of thes cosmic clouds,typically 1,000 times the size of ou solar system,evoke their popular names Flipping through digital pictures made byparticipants in the Kitt PeakNational Observatory Visitor Center' Advanced Observing Program,astronomer Adam Block created thisdelightful animation.Ten different planetary nebula images are presented, each registeredon the central star.In order, their catalog designations ar NGC1535 NGC 3242 (Ghost of Jupiter) NGC 6543 (Cat's Eye) NGC 7009 (Saturn Nebula) NGC 2438 NGC 6772 Abell 39 NGC 7139 NGC 6781,and M97 (Owl Nebula).This glorious final phasein the life of a star lasts only about 10,000 years.

A Flying Astronaut Over Earth

What would it be like to fly free over the seas and clouds of Earth?In 1994 astronaut Mark Lee found out when he tested the Simplified Aid for EVA Rescue (SAFER) system for NASA. SAFER is a backpack propulsion unit that incorporates small nitrogen thrusters controlled by hand and moderated by computer. Pictured, Lee jets about the bay of Space Shuttle Discovery, over 200 kilometers above Earth in the first u tethered space walk in ten years.Lee was not in danger -- the shuttle could have been used to retrieve him SAFER, smaller than the Manned Maneuvering Unit, is designed as a backup system to help astronauts in the unlikely event that they become too separated from their work outside the International Space Station.

A Global Dust Storm on Mars

A dust storm on Mars can involve nearly the entire planet. As spring descended on the southern hemisphere of the red planet this June and July, a global dust storm raged. Pictured above is the storm on July 8 as it spread up from the south, oriented on the lower right. The image was captured by the robot Mars Global Surveyor spacecraft which continues to orbit the red planet. A smaller dust storm is visible in the north to the left of the dark giant volcano Ascraeus Mons. Far-reaching dust storms also occur on planet Earth.

IC 418 The Spirograph Nebula

What is creating the strange texture of IC 418? Dubbed the Spirograph Nebula for its resemblance to drawings from a cyclical drawing tool, planetary nebula IC 418 shows patterns that are not well understood. Perhaps they are related to chaotic winds from the variable central star, which changes brightness unpredictably in just a few hours. By contrast, evidence indicates that only a few million years ago, IC 418 was probably a well-understood star similar to our Sun. Only a few thousand years ago, IC 418 was probably a common red giant star. Since running out of nuclear fuel, though, the outer envelope has begun expanding outward leaving a hot remnant core destined to become a white-dwarf star, visible in the image center. The light from the central core excites surrounding atoms in the nebula causing them to glow. IC 418 lies about 2000 light-years away and spans 0.3 light-years across. This recently released false-color image taken from the Hubble Space Telescope reveals the unusual details.

The Iron Sun

Theultraviolet light emitted by eleven times ionized iron at temperaturesover 2 million degrees Farenheit was used to record the above picture of theSun on September 22, the date of theautumnal equinox.The image was made b the EIT camera onboar the SOHO spacecraft, a space observatory which can continuousl observe the Sun.Eleven times ionized iron i atomiciron with eleven of its electrons stripped away.Here the electrons are stripped by thefrantic collisions with other atoms and electronswhich occur at the extreme temperatures i theSolar Corona.Since electrons are negatively charged, theresulting ionized iron atom is highl positively charged.Astronomer's "shorthand" for eleven times ionized iron is written"Fe XII", the chemicalsymbol for iron followed by Romannumeral 12 (Fe I is neutral iron).

NGC 6992 A Glimpse of the Veil

After 5,000 years, the gorgeou VeilNebula is still turning heads.Cataloged as NGC 6992, these glowin filaments of interstellarshocked gas are part of a larger spherica supernova remnant known as th Cygnus Loop or theVeil Nebula -- expanding debris from a star whic exploded over 5,000 years ago.This color digital image of bitof the Veil has been processedand enhanced to reveal stunning details in the diaphanous cosmic cloud.Seen from our perspective against a rich Milky Way star field,the Veil Nebula i nowknown to lie some 1,400 light-years away toward theconstellation Cygnus.At that distance witnessesto the original stellar explosion would haveseen a star in the heavensincrease in brightness to about -8 magnitude, roughly corresponding tothe brightness of the crescent Moon.

Elements of Nearby Spiral M33

Spiral galaxy M33 is a mid-sized member of our Local Group of Galaxies. M33 is also called the Triangulum Galaxy for the constellation in which it resides. About four times smaller (in radius) than our Milky Way Galaxyand the Andromeda Galaxy (M31), it is much larger than the many of the local dwarf spheroidal galaxies. M33's proximity to M31 causes it to be thought by some to be a satellite galaxy of this more massive galaxy. M33's proximity to our Milky Way Galaxy causes it to appear more than twice the angular size of the Full Moon, and bevisible with a good pair of binoculars.The above high-resolution image highlights light emitted by hydrogen in red and oxygen in blue. It was taken to help separate stars from emission nebulae, and therefore help study how galaxies form stars.

Comet Borrelly's Nucleus

What does a comet nucleus look like? To answer this question, NASAcontrollers drove an aging probe through the hostile environsof a distant comet, expecting that even if comet fragmentsdisabled the spacecraft, it would be worth the risk. The probe, DeepSpace 1, survived. Pictured above is the mostdetailed image ever taken of a comet nucleus,obtained Saturda by Deep Space 1 andreleased yesterday by NASA. CometBorrelly's nucleus is seen to be about 8 kilometers long wit mountains, faults, grooves, smooth rolling plains, and materials of vastly different reflectance. Light colored regions are presentnear the center and seem to give rise to dust jets seen in Borrelly' coma, visible in distant images of the comet. Previously, the best image of a comet nucleus came from the Giottomission to Comet Halley in 1986. Deep Space 1 images of Borrelly add welcomed bedrock to understanding Solar System historyand to the accurate prediction of future brightness changes of notoriously fickle comets.

The Highs and Lows of Earth

What's up on planet Earth? A truly global answer has now been created by the Global Land One-km Base Elevation (GLOBE) Project. Pictured above is the best digital elevation map yet created for our home planet, a map it took over ten years to make that incorporates data provided by many different countries around the world. The relief map is color coded with sea level shown in black, relatively low areas shown in green, higher areas shown in brown, and the highest areas shown in white. Can you find your hometown? Clicking on the map will bring up a higher resolution version. Even more detailed versions are also available.

A Solar Prominence Erupts

Our Sun is still very active. Last year, our Sun went though Solar Maximum, the time in its 11-year cycle where the most sunspots and explosive activities occur. Sunspots, the Solar Cycle, and solar prominences are all caused by the Sun's changing magnetic field. Pictured above is a solar prominence that erupted on May 15, throwing electrons and ions out into the Solar System. The image was taken in the ultraviolet light emitted by a specific type of ionized helium, a common element on the Sun. Particularly hot areas appear in white, while relatively cool areas appear in red. Our Sun should gradually quiet down until Solar Minimum occurs in 2007.

Molecular Cloud Barnard 68

Where did all the stars go? What used to be considered a hole in the sky is now known to astronomers as a dark molecular cloud. Here, a high concentration of dust and molecular gas absorb practically all the visible light emitted from background stars. The eerily dark surroundings help make the interiors of molecular clouds some of the coldest and most isolated places in the universe. One of the most notable of these dark absorption nebulae is a cloud toward the constellation Ophiuchus known as Barnard 68, pictured above. That no stars are visible in the center indicates that Barnard 68 is relatively nearby, with measurements placing it about 500 light-years away and half a light-year across. It is not known exactly how molecular clouds like Barnard 68 form, but it is known that these clouds are themselves likely places for new stars to form.

Full Throttle For Deep Space 1

At full throttle th Deep Space 1 spacecraft' innovative ion driveproduces about 1/50th of a pound of thrust ... a force so greatthat it woul just abouthold up a piece of paper on planet Earth!Still, powered by solar array ion propulsionsystems can run continuously.For long duration space missions they ultimatel win outover the powerfulbut brief blasts of less efficien chemical rockets.Deep Space 1 i seen here suspended in an assembly room, a folde solar arrayresting above the circular ion propulsion module.Already a successfu technologydemonstrator with experimenta autonomous software,the spacecraft flew b asteroid 9969 Braille in July of 1999.Later that year, in November, the robot probe wasnearly lost due to the failure of its wide-field star tracker camera.But engineers were able to reprogram the navigationsystem to utilize another on-board camera and on 28 June 2000the ion drive was throttled up.Now, th adventuresof Deep Space 1 continue Againsteering by the stars, Deep Space isscheduled to rendezvous with periodi CometBorrelly today.

Where a Black Hole Roams

Black hole candidate XTE J1118+480 is known to roam the haloof our Milky Way Galaxy This exoticsystem - thought to be stellar mass black hole consumingmatter from a companion star - was discovered only last year as aflaring celestial x-ray source.Suggestively termed microquasar,recent radio and archival optical observations o itsmotion through the sky have now allowed it orbit to be calculated.Illustrated above, th black hole's present galactic location isindicated by the purple dot, with th Sun's position in yellow.A mere 6,000 light-years from the Sun now, XTE J1118+480's orbit istraced by the orange line, backtracked for some 230 million years intothe past based on models of the Galaxy.Astronomers note this black hole's orbit about the galactic center,looping high above and belo the Galaxy'splane of gas, dust,and stars,is similar to orbits of globula star clusters ancient denizens of our Galaxy.It seems likely tha XTE J1118+480 too has its origins in the earl history andhalo of the Milky Way.

X Ray Stars in M15

Side by side, tw x-ray stars greeted astronomers inthis false-color Chandra Observator x-ray image of aregion near the core of globular starcluster M15.The greeting was a pleasant surprise, as all previous x-rayimages of the cluster showed only one such source wher Chandra'ssharper x-ray vision now reveals two.These x-ray sources are modeled a neutron starbinary systems.Each is a city-sized neutron star in close orbit witha normal stellar companion X-rays are generatedas matter from the normal sta falls ontothe compact neutron star This break through explainswhy observations of thepreviously recognized lone neutron star binary system in M15were difficult to reconcile with any single model.It also suggests that other globular star clusters whic roam the haloof our Milky Way galaxy an seem to containonly one such neutron star x-ray source may in fac contain more.An optical Hubble Space Telescope image of the dens M15 cluster is inset at the upper right.

SIRTF Name This Satellite

NASA is preparing to launch its next Great Observatory in 2002, but it does not yet have a proper name. Can you help? Currently referred to only as the Space Infrared Telescope Facility (SIRTF), NASA seeks to add something more significant. Previously, NASA named its Great Observatories for scientists of the recent past, including the Hubble Space Telescope, the Compton Gamma Ray Observatory and the Chandra X-ray Observatory. SIRTF will be the most powerful infrared telescope ever launched, imaging everything from nearby planetary disks to distant galaxies. To enter the contest, one must conform to all rules including the submission of an essay of 250 words or less. The contest ends on December 20.

Surrounded by Mars

Just after landing on Mars in 1997, the robotic Mars Pathfinder main station took a quick first look around. This insurance panorama was taken even before the Sagan Memorial Station camera was raised to its two-meter-high perch. The full view is best seen by slowly scrolling to the right. The unique perspective captures many Mars Pathfinder instruments in the close foreground including a screen for judging sky illumination, communications antennae, solar panels, and two ramps leading down to the surface for the robot probe Sojourner. After taking the ramp on the right, Sojourner can be seen on the Martian surface. Visible on the surface are numerous rocks and hills that came to be better studied. The Mars Pathfinder mission went on to return 16,000 images and data that resulted in many discoveries, including evidence for warmer and wetter conditions on Mars in the past. After nearly three spectacular months exploring the surface, Mars Pathfinder dropped out of communication, likely the result of depleted battery power.

Southwest Andromeda

This new image composite of the southwest region of M31 from the Subaru Telescope shows many stars, nebulae, and star clusters never before resolved. An older population of stars near Andromeda's center causes the yellow hue visible on the upper right. Young blue stars stand out in the spiral arms on the lower left. Red emission nebula, blue open clusters of stars, and sweeping lanes of dark dust punctuate the swirling giant. Andromeda, at about 2.5 million light years distant, and our Milky Way are the largest galaxies in the Local Group of Galaxies. Understanding M31 helps astronomers to understand our own Milky Way Galaxy, since the two are so similar.

Friday, 27 June 2008

Venus Once Molten Surface

If you could look at Venus with radar eyes - this is what you might see.This computer reconstruction of the surface of Venus was created from data from the Magellan spacecraft. Magellan orbited Venus and used radar to map our neighboring planet's surface between 1990 and 1994 Magellan found many interesting surface features, including the large circular domes, typically 25-kilometers across, that are depicted above. Volcanism is thought to have created the domes, although the precise mechanism remains unknown. Venus' surface is so hot and hostile that no surface probe has lasted more than a few minutes.

Eclipsed Moon in Infrared

The total lunar eclipse of September 1996disappointed many observers in North America whowere cursed with cloudy skies.However, th MidcourseSpace Experiment (MSX) satellite hada spectacular view from Earth orbit an SPIRIT III,an onboard infrared telescope, was used torepeatedly image the moo during the eclipse.Above is one ofthe images taken during the 70 minute totality, the Moon completel immersed inthe Earth's shadow.Infrared ligh has wavelengthslonger than visible light - human's can not see it but feel it as heat.The bright spots correspond to the warm areas on thelunar surface, dark areas are cooler.The brightest spot below and left of center is th crater Tycho,the dark region at the upper right i the Mare Crisium.The series of SPIRIT III images allow the determination of coolingrates for geologically different areas, exploring the physical propertie of the Moon's surface.

Cold Dust in the Eagle Nebula

Stars are born i M16's EagleNebula, a stellar nursery 7,000 light-years from Earthtoward the constellatio Serpens.The striking nebula' star forming pillars of gas and dust ar familiar to astronomersfrom images at visible wavelengths, bu this false-color pictureshows off the nebula i infrared light.Data from ESA' Infrared Space Observatorysatellite (ISO) was used to construct the detaile twocolor image, dominated by infrared emission fromclouds of interstellar material at temperatures below -100degrees Celsius.Blue colors highlight emission thought to indicate the presence of complexcarbon molecules, known on planet Eart as PAHs, whilered colors trace emission from cold, microscopi dust grains.Hot young stars are formed as this frigid material condenses under theinfluence of gravity.Once begun, the process takes only tens of thousands of years fortruly massive stars and up to tens of millions of years for low massstars like the Sun.

X-Rays and the Circinus Pulsar

A bizarr stellarcorpse 19,000 light-years from Earth pulsarPSR B1509-58beckons from the small southern constellatio of Circinus.Like its cousin at the heart of the Crab nebula,the Circinus pulsar is a rapidly spinning, magnetize neutron star.Seen in this false-color Chandra Observatoryimage, the environmentsurrounding this cosmic powerhouse glows in high energy x-rays.The Circinu pulsar itself, thought to generate more than7 quadrillionvolts (7 followed by 15 zeros), lies within the knot of brightemission near the center of the picture. Stretching toward the bottom left x-rayemission traces jet of particles almost 20 light-years longthat seems to arise from the pulsar's south pole,while the arc of bright emissionabove the central knot is likely a shockwave produced by particlesdriven from the pulsar's equator.Near the top of the picture, lower energy x-ray emission shown in greenis from gas shock-heated to millions of degrees Celsius.The shocked gas was produced by debri blasted out fromthe stellar explosion thatcreated the Circinus pulsar.

Zodiacal Light and the False Dawn

An unusual triangle of light will be particularly bright near the eastern horizon before sunrise during the next two months for observers in Earth's northernhemisphere. Once considered a false dawn, this triangle of light is actually Zodiacal Light, light reflected from interplanetary dust particles. The triangle is clearly visible on the left of the above frame taken from Mauna Kea in Hawaii on August 30 by one of the developing global network of fisheye nighttime web cameras called CONCAMs. Zodiacal dust orbits the Sun predominantly in the same plane as the planets: the ecliptic. Indeed, the triangle points to bright spots Jupiter and Saturn, with Saturn nearer the center. Zodiacal light is so bright this time of year because th dust band is oriented nearly vertical at sunrise, so that the thick air near the horizon does not block out relatively bright reflecting dust. Zodiacal light is also bright forpeople in Earth's northern hemisphere in March and April just after sunset.

Spiral Galaxy NGC 3310 Across the Visible

The party is still going on in spiral galaxy NGC 3310. Roughly 100 million years ago, NGC 3310 likely collided with a smaller galaxy causing the large spiral galaxy to light up with a tremendous burst of star formation. The changing gravity during the collision created density waves that compressed existing clouds of gas and triggered the star-forming party. The above image composite by the Hubble Space Telescope was used to find the ages of many of the resulting clusters of stars. To the surprise of many, some of the clusters are quite young, indicating that starburst galaxies may remain in star-burst mode for quite some time. NGC 3310 spans about 50,000 light years, lies about 50 million light years away, and is visible with a small telescope towards the constellation of Ursa Major.

Galactic Center Flicker Indicates Black Hole

Why would the center of our Galaxy flicker? Many astronomers believe the only credible answer involves a black hole. During observations of Sagittarius A* with the orbiting Chandra X-ray Observatory, the bright X-ray source at the very center of our Milky Way brightened dramatically for a few minutes. Sagittarius A* is visible as the bright dot near the center of the above image. Since large objects cannot vary quickly, a small source is implicated in the variation. Evidence including the motions of central stars indicates that the center of our Galaxy is a massive place, however, estimated to be over a million times the mass of our Sun. Only one known type of object can fit so much mass in so small a volume: a black hole. This short flicker therefore provides additional evidence that a black hole does indeed reside at our Galaxy's center. If true, the flicker might have been caused by an object disrupting as it fell toward the disruptive monster.

NGC 3293 A Bright Young Open Cluster

Hot blue stars shine brightly in this beautiful, recently formed galactic or "open" star cluster. Open cluster NGC 3293 is located in the constellation Carina, lies at a distance of about 8000 light years, and has a particularly high abundance ofthese young bright stars. A study of NGC 3293 implies that the blue stars are only about 6 million years old, whereas thecluster's dimmer, redder stars appear to be about 20 million years old. If true, star formation in this open cluster took at least 15 million years. Even this amount of time is short, however, when compared with the billions of years stars like our Sun live,and the over-ten billion year lifetimes of many galaxies and our universe. NGC 3293 appears just in front of a dense dust laneemanating from the Carina Nebula.

Moon Occults Saturn

On September 18, 1997, many stargazer in the U. S. were able to watch a lovelyearly mornin lunar occultation a a bright Moonpassed in front of Saturn Using a 1.2 meter reflector, astronomerKris Stanek had a excellent view of this dream-like event from th WhippleObservatory atop Arizona' Mount Hopkins.This animated gif image was constructed by Wes Colleyfrom 4 frames taken by Stanekat 35 second intervals as the ringed planet emerged from behin the Moon's dark limb While lunar occultations of fairly bright starsand planets are not extremely rare events, thei exacttiming depends critically on the observer's location.For observers i westernNorth America, the Moon will nextoccult Saturn on Monday morning September 10.

Moon AND Sun

Today's composite image was made from 22 separate picturesof the Moon and Sun all taken fro Chisamba, Zambia during thetotal phase of the 2001 June 21 solar eclipse.The multiple exposureswere digitally processed and combined tosimultaneously show a wealth of detail which no single cameraexposure or naked-eye observation could easily reveal.Most striking are the incredible flowing streamersof the Sun's outer atmosphere o solar corona, notoriously difficult to see except whe thenew Moon blocks the bright solar disk.Features on the darkened near sid of the Moon canalso be made out illuminatedby sunlight reflected fro afull Earth.A giant solar prominence seems to hangjust beyond the Moon's eastern (left) edge while about onediameter farther east of the eclipsed Sun is th relatively faint (4th magnitude)star 1 Geminorum.

Moon AND Stars

Here's something you don't see too often ... a detailed picture of thefull Moon surrounded by a rich field of background stars. It's true that bright moonlight scattered by the atmosphere tends tomask faint stars, but pictures of th sunlit portionof the Moon madewith earthbound telescopesor even with cameras on th lunar surface often fail to show any backgroun stars at all.Why? Because the exposure times are too short.Very short exposures, lasting fractions of a second, are required toaccuratel recordan image of the bright lunar surface.But the background stars (and galaxies!) such as those visible aboveare much fainter and need exposures lasting minutes to hours whichwould seriously overexposethe surface of the Moon.So, of course this stunning viewreally is a combination of two digital images --a short exposure, registering the exquisite lunarsurface detail at full Moon, superposed ona separate very long exposure, made wit the Moon absent from the star field.The final representatio ofMoon and background stars is verydramatic, even though it could not have been captured in a singleexposure.

3C175 Quasar Cannon

3C175 is not only a quasar, it is a galaxy-fueled particle cannon. Visible as the central dot is quasar 3C175, the active center of a galaxy so distant that the light we see from it was emitted when the Earth was just forming. The above image was recorded in radio waves by an array of house-sized telescopes called the Very Large Array (VLA). Shooting out from 3C175 is a thin jet of protons and electrons traveling near the speed of light that is over one million light-years long. The jet acts like a particle cannon and bores through gas cloud in its path. How this jet forms and why it is so narrow remain topics of current research.

2dF Sees Waves of Galaxies

How are galaxies distributed in the universe? This question is of more than aesthetic interest because the answer likely holds clues to composition of the universe itself. The above map shows the distribution of nearly 200,000 galaxies and is the latest answer obtained by one of the most complex astronomical instruments yet created: the Two-Degree Field (2dF) system. The 2dF system measures galaxy redshifts, allowing astronomers to estimate distances to some of the millions of galaxies visible, and hence to make a three-dimensional map of the local universe. Although the distribution of galaxies appears nearly uniform on the largest scale, waves of galaxies are discernable extending up to 100 million light-years. Detailed analyses of the incoming data indicate that to create such a network of waves, normal baryonic matter must make up only 15 percent of all matter, while all matter must make up only about 30 percent of that needed to make the universe geometrically flat. Is the remaining 70 percent dark energy?

Thursday, 26 June 2008

The Making of the Rotten Egg Nebula

Fast expanding gas clouds mark the end for a central star in the Rotten Egg Nebula. The once-normal star has run out of nuclear fuel, causing the central regions to contract into a white dwarf. Some of the liberated energy causes the outer envelope of the star to expand. In this case, the result is a photogenic proto planetary nebula. As the million-kilometer per hour gas rams into the surrounding interstellar gas, a supersonic shock front forms where ionized hydrogen and nitrogen glow blue. The complex shock front had been hypothesized previously but never so clearly imaged. Thick gas and dust hide the dying central star. The Rotten Egg Nebula, also known as the Calabash Nebula and OH231.8+4.2, will likely develop into a full bipolar planetary nebula over the next 1000 years. The nebula, pictured above, is about 1.4 light-years in extent and located about 5000 light-years away toward the constellation of Puppis.

Deimos A Small Martian Moon

Mars has two tiny moons, Phobos and Deimos. Pictured above is Deimos, the smaller moon of Mars. In fact, Deimos is one of the smallest known moons in the Solar System measuring only nine miles across. The diminutive Martian moons were discovered in 1877 by Asaph Hall, an American astronomer working at the US Naval Observatory in Washington D.C. The existence of two Martian moons was predicted around 1610 by Johannes Kepler, the astronomer who derived the laws of planetary motion. In this case, Kepler's prediction was not based on scientific principles, buthis writings and ideas were so influential that the two Martian moons are discussed in works of fiction such as Jonathan Swift's Gulliver's Travels, written in 1726, over 150 years before their actual discovery.

Magnetars In The Sky

Indicated on thi infrared image of the galactic center regionare positions of candidate magnetars - believed to bethe strongest magnets in the galaxy.Classified by observers as Soft Gamma Repeaters SGRs) and Anomalous X-ray Pulsars AXPs), these cosmic powerhouses are likel city-sized,spinning, highly-magnetized neutron stars.How strong is a magnetar's magnetic field The Earth's magnetic fieldwhich deflect compass needles is measuredto be about 1 Gauss, whilethe strongest fields sustainable in earthbound laboratories areabout 100,000 Gauss.A magnetar' monster magnetic fieldis estimated to be as high as 1,000,000,000,000,000 Gauss A magnet this strong, located at abouthalf the distance to the Moonwould easily erase your credit cards and suck pens out of your pocket.In 1998, from a distance of about 20,000 light-years, one magnetar SGR 1900+14 generate a powerful flash of gamma-rays detectedby many spacecraft That blast of high-energy radiation is now known to havehad a measurable effect on Earth's ionosphere At the surface of the magnetar,its powerful magnetic field is thought to buckle and shift the neutronstar crust generating the intense high-energy flares.

The Flight of Helios

Solar-powered,remotely piloted, and flying at about 25 miles per hour,NASA's Heliosaircraft, i picturedabove at 10,000 feet in skies northwest of Kauai, Hawaii on August 13.This ultralight propeller driven aircraft, essentially a flying wingwith 14 electric engines, was built b AeroVironment Inc.Covered with solar cells, Helios' impressive 247 foot wide wingexceeds the wing span and even overall length of Boeing747 jet airliner.Climbing during daylight hours, the prototype aircraf ultimatelyreached an altitude just short of 100,000 feet,breaking records for non-rocket powere flight.Helios is intended as a technology demonstrator, butregular, long-duration flights at that altitudecould be used for environmental monitoringmissions and, communications relays.In the extremely thin air 100,000 feet above Earth's surface, the flightof Helios als simulatesconditions fo wingedflight in th atmosphereof Mars.

How Big Is 2001 KX76?

Newly discoveredminor planet 2001 KX76 is circled in the top panelabove, a recent composite image from the European SouthernObservatory's 2.2 meter telescope a La Silla, Chile.Though 2001 KX76 appears here as single point of light in anunremarkable star field its orbit has been accurately measured b Astrovirtel,a newly operational "virtual telescope" capable of miningmany years of archival data for previously unrecognized imagesof 2001 KX76.The results show thi minorplanet to be very distant, now orbiting just beyon Pluto and Charon in th realmof the Kuiper Belt.At its distance, apparent brightness, and assuming a reasonablesurface reflectivity 2001KX76 would be 1,200 kilometers or more across -- larger thanthe largest main-bel asteroid, Ceres.In fact, the illustration in the bottom panel graphicallycompares this size estimate to Pluto, Charon, and the largestpreviously know Kuiper Belt objects, indicating the newfoun minor planetis second only to Pluto in diameter.Along with other evidence, the comparison suggest thatPluto and Charon are closely related t KuiperBelt worlds like 2001 KX76.

AFGL 2591 A Massive Star Acts Up

Young star AFGL 2591 is putting on a show. The massive star is expelling outer layers of dust-laced gas as gravity pulls inner material toward the surface. AFGL 2591 is estimated to be about one million years old -- much younger than our own Sun's 5 billion-year age -- and has created a nebula over 500 times the diameter of our Solar System in just the past 10,000 years. The above image in infrared light is one of the first from the new NIRI instrument mounted on one of the largest ground-based optical telescopes in the world: Gemini North. Sharp details are discernable that are blocked by opaque dust in visible-light images. Close inspection of the image reveals at least four expanding rings, indicating an episodic origin to the mysterious activity. AFGL 2591 lies about 3000 light years away toward the constellation of Cygnus.

Jagged Hills on Jupiters Callisto

Why does Jupiter's moon Callisto have unusual jagged hills? This mystery came to light after the robot spacecraft Galileo, in orbit around Jupiter since 1995, swooped past the dark moon in May. The resulting pictures were the highest resolution yet obtained for a Jovian moon: objects as small as 3 meters across are discernable. The strange landscapes pictured above show areas rich in bright sharp mounds about 100 meters tall. A likely formation hypothesis holds that these hills are the result of ejecta thrown billions of years ago during a violent impact. The lower inset region apparently has undergone an epoch of relatively high ice erosion, where dark rock has filled in some of the inter-hill regions. NASA has recently cleared Galileo to continue swooping Jupiter's moons until 2003, when it will end its journey with a spectacular dive into Jupiter's atmosphere.

Artificial Night Sky Brightness

Where have all the dim stars gone? From many places on the Earth including major cities, the night sky has been reduced from a fascinating display of hundreds of stars to a diffuse glow through which only a handful of stars are visible. The above map indicates the relative amount of light pollution that occurs across the Earth. The cause of the pollution is artificial light reflecting of molecules and aerosols in the atmosphere. Parts of the Eastern United States and Western Europe colored red have an artificial night sky glow over nine times that of the natural sky. In any area marked orange or red, the central band of our Milky Way Galaxy is no longer visible.The International Dark Sky Association suggests common types of fixtures that provide relatively little amounts of light pollution.

Uranus The Tilted Planet

Uranus is the third largest planet in our Solar System after Jupiter and Saturn. Uranus is composed mostly of rock and ices, but with a thick hydrogen and helium atmosphere.The blue hue of Uranus' atmosphere arises from the small amount of methane which preferentially absorbs red light. This picture was snapped by th Voyager 2 spacecraft in 1986 - the only spacecraft ever to visit Uranus. Uranus has many moons and a ring system. Uranus, like Venus, has a rotation axis thatis greatly tilted and sometimes points near the Sun. It remains an astronomical mystery why Uranus' axis is so tilted. Uranus and Neptune are quite similar: Uranus is slightly larger but less massive.

Pioneer 10 The First 7 Billion Miles

Q: What was made by humans and is 7.3 billion miles away?A: Pioneer 10 --and 1997 was the25th anniversary of its launch.Almost 11 light-hours distant Pioneer 10 is presently about twice as far from the Sunas Pluto, an bound for interstellar spaceat 28,000 miles per hour.The distinction of being the first human artifact to ventur beyond the known planets of the Solar System isjust one in a long list of firsts forthis spacefaring ambassador, including;the first spacecraft to travel through the asteroid beltand explore the outer Solar System,the first spacecraft t visitJupiter,and the first to use a planet' gravityto change its course and to reach solar-system-escape velocity Pioneer 10's mission is nearing an end.Now exploring the distant reache of the heliosphereit will soon run out of sufficientelectrical power to operate science instruments.However the570 lb. spacecraft will continue to coast andin 300,000 years or so it will pass within about 3 light year ofnearby star Ross 248.Ross 248 is a faint red dwarf just over 10 light years distant inthe constellation Taurus.(Note: In 1998 Voyager 1, launched 5 years later but travelingfaster than Pioneer 10, became humanity's most distant spacecraft.)

NEAR at Eros Before Touchdown

On 12 February, 2001, th NEAR-Shoemakerspacecraft gentlytouched-down on the the surface of Eros -- thefirst ever landingon an asteroid.During the descent, the spacecraft's camera recorde successiveimages of th diminutive world's surface, revealing fractured boulders,dust filled craters, and a mysterious collapsed channel Thelast frame, seen in the above montage at the far left, wastaken at a range of 128 meters.Expanded in the inset, it shows surface featuresa few centimeters across Stereoexperimenter Patrick Vantuyne, constructed this montage from thefinal images in the landing sequence, carefully identifying theoverlapping areas in successive frames.Frames which overlap were taken by the spacecraft fromslightly differen viewpoints,allowing Vantuyneto construct close-up stereo imagesof the surface o asteroid 433 Eros.

Distortion from a Distant Cluster

This stunningcolor deep sky view toward the constellation Pisces wasmade with data from a fast, sensitive, digital detector known as th BigThroughput Camera operating a Cerro TololoInter-American Observatory in Chile.Hardly noticeable in the original picture is the smallcluster of about 15 galaxies nearly 3 billion light-year distant,circled at the lower right.In fact, this distant cluster was not discovered by noticingits appearance in the image at all, but instead by mappingthe subtle distortions created by its gravity.As predicted b Einstein's General Relativity theory,the cluster's gravitational mass acts like a lens, bending lightand distorting the shape of background galaxies.The effect is known as gravitational lensing.Compute mapping ofweak distortions of background galaxy shapesacross the Big Throughput image revealed that the large scaledistribution of mass in that part of the sky was concentrated in asmall region.That region turned out to correspond to the galaxycluster -- the first time such an objec hasbeen discoveredon the basis of its mass properties rather than its light.

The Bubbling Cauldron of NGC 3079

Edge-onspiral galaxy NGC 3079 is a mere 50 million light-years awaytoward the constellation Ursa Major Shown in thisstunning false-colo Hubble Space Telescopeimage, the galaxy's disk - composed of spectacularstar clusters in winding spiral arms and dramaticdark lanes of dust spanssome 70,000 light-years.Still, NGC 3079's most eye-catching features are the pillars of gaswhich tower above a swirling cosmic cauldron of activityat the galaxy's center.Seen in the close-up inset at lower right, the pillars rise to aheight of about 2,000 light-years and seem to lie on the surfaceof an immense bubble rising from the galactic core.Measurements indicate that the gaseous pillars are streaming awayfrom the core at 6 million kilometers per hour What makes this galaxy' cauldron bubble Astronomersare exploring thepossibility that the superbubble i formedby winds from massive stars.If so, these massive stars were likely born all at once as thegalactic center underwent sudden burst of star formation.

Dark Spots on Neptune

Neptune has spots. The Solar System's outermost gas giant shows a nearly uniform blue hue created by small amounts of methane drifting in a thick atmosphere of nearly colorless hydrogen and helium. Dark spots do appear, however, that are anti-cyclones: large high-pressure systems that swirl in Neptune's cold cloud tops. Two dark spots are visible in the above picture taken by the robot Voyager 2 spacecraft in 1989: an Earth-sized Great Dark Spot located on the far left, and Dark Spot 2 located near bottom. A bright cloud dubbed Scooter accompanies the Great Dark Spot. Recent computer simulations indicate that scooters are methane clouds that might commonly be found near dark spots. Subsequent images of Neptune by the Hubble Space Telescope in 1994 indicated that both of these dark spots had dissipated, but another had been created.

The Lagoon Nebula in Three Colors

The bright Lagoon Nebula is home to a diverse array of astronomical objects. Particularly interesting sources include a bright open cluster of stars and several energetic star-forming regions. When viewed by eye, cluster light is dominated by an overall red glow that is caused by luminous hydrogen gas, while the dark filaments are caused by absorption by dense lanes of dust.The above picture, from the Curtis-Schmidt Telescope,however, shows the nebula's emission in three exact colorsspecifically emitted by hydrogen, oxygen, and sulfur.The Lagoon Nebula, also known as M8 and NGC 6523, lies about 5000 light-years away. The Lagoon Nebula can be located with binoculars in the constellation of Sagittarius spanning a region over three times the diameter of a full Moon.

Mercury A Cratered Inferno

Mercury's surface looks similar to our Moon's. Each is heavily cratered and made of rock. Mercury's diameter is about 4800 km, while the Moon's is slightly less at about 3500 km (compared with about 12,700 km for the Earth). But Mercury is unique in many ways. Mercury is the closest planet to the Sun, orbiting at about 1/3 the radius of the Earth's orbit. As Mercury slowly rotates, its surface temperature varies from an unbearably cold -180 degrees Celsius to an unbearably hot 400 degrees Celsius. The place nearest the Sun in Mercury's orbit changes slightly each orbit - a fact used by Albert Einstein to help verify the correctness of his then newly discovered theory of gravity: General Relativity. The above picture was taken by the only spacecraft ever to pass Mercury: Mariner 10 in 1974.

Phobos Doomed Moon of Mars

Mars,the red planet named forthe Roman god of war, has two tiny moons Phobos an Deimos,whose names are derived from the Greek for Fear and Panic.Thes Martianmoons may well be capture asteroidsoriginating in the main asteroid belt between Marsand Jupiter or perhaps from even moredistant reaches of th Solar System.In this 197 Viking 1 orbiter image,the largest moon, Phobos, is indeed seen to be aheavily cratered asteroid-like object.About 17 miles across, Phobos reallyzips through the Martian sky.Actually rising above Mars' western horizon and setting in the east,it completes an orbit in less than 8 hours.But Phobos is doomed.Phobos orbits so close to Mars,(about 3,600 miles above the surface compared to 250,000 miles fo our Moon)that gravitational tidal forces are dragging it down.In 100 millionyears or so it will likely crash into the surface or be shattered by stresscaused by th relentlesstidal forces, the debris forming a ring around Mars.

The 47 Ursae Majoris System

Watching and waiting,astronomers have uncovered the presence of morethan 70 planets orbiting stars other than the Sun.So far almost all thes extrasolarplanets have crazy elongated orbits,lie uncomfortably close to their parent stars, or are found in bizarre,inhospitable systems.Yet a reported new planetdiscovery indicates for the first time that anearby sun-like star, 47 Ursae Majoris (47 UMa), has atleast two planets in nearly circular orbits more reminiscent o Jupiter an Saturn in our ow familiarSolar System.The planets are too distant and faint to be photographed directly Still, 13 years ofspectroscopic observations of 47 UMa have reveale the wobblingsignature of a second plane intertwined with onepreviously known In this artist'sillustration, the worldsof 47 UMa hang over the rugged volcanic landscape ofa hypothetical moon.The moon orbits th newlydiscovered planet, imagined here withSaturn-like rings, while the previously known planet is visible as atiny crescent, close to the yellowish star.Closer still to 47 UMa is another tiny dot, hypothetical Earth-lik water world.About 51 light-years distant, 47 UMa can be found in planet Earth'ssky near the Big Dipper.

Centaurus A X-Rays from an Active Galaxy

Its core hiddenfrom optical view by a thick lane of dust, the giant elliptica galaxy Centaurus A was among the first objectsobserved by the orbiting Chandra X-ray Observatory.Astronomers were not disappointed, as Centaurus A'sappearance in x-rays makes its classification as a active galaxy easy to appreciate.Perhaps the most striking feature o thisChandra false-color x-ray viewis the jet, 30,000 light-years long.Blasting toward the upper left corner of the picture the jetseems to arise from the galaxy's bright central x-ray source --suspected of harboring a black hole with a million or so timesthe mass of the Sun Centaurus Ais also seen to be teeming with otherindividual x-ray sources and a pervasive, diffus x-ray glow.Most of these individual sources are likely to be neutron starsor solar mass black holes accreting material from their lessexotic binary companion stars.The diffuse high-energy glowrepresents gas throughout the galaxyheated to temperatures of million of degrees C.At 11 million light-years distant in the constellatio Centaurus,Centaurus A (NGC 5128) is the closes active galaxy.

Mars 3-D Dunes

Get out your red/blue glasses and treat yourself to this dramatic3-D view of sand dune on Mars!The field of undulating dunes is found inNili Patera, a volcanic depression in centra Syrtis Major,the most prominent dark featur on the Red Planet.Two different images from the orbiting Mars Global Surveyorspacecraft were combined to mak this stereo picture,one taken in March 1999 and the other recorded in April 2001.Sculpted by winds like the sand dune of Earth,these particularMartian dunes show no change in shape over th time separating thetwo images, a period equivalent to abou one Martian year.This cropped version of th 3-Dpicture spans an area around 2 kilometers across.Walking, you might cover that distance in about20 minutes.

X-Rays from the Galactic Plane

In February 2000, the orbitin Chandra X-ray Observatory spent 27 hour staring into the planeof our Milky Way galaxy.Its target was a spot in the smal constellation Scutum, within the Milky Way' zone of avoidance where galacticgas and dust clouds block visible light, making a poorwindow for optical telescopes.However the penetrating x-ray observations looked throughthe obscurations revealing the Milky Way and the Universe beyond The x-ray view isreconstructed above in false color.Distant active galaxiesemitting high energy x-rays appear as blue dots,while reddish dots are sources of lower energy x-rays,likely stars within th Milky Way itself.Intriguing is th diffuse blue glow of high energy x-rays,distinct from the individual sources in the picture Astronomers havelong debated whether our galactic plane's apparentlyextended x-ray emissionwas due to discrete sources or diffuse hot gas As these resultssuggest diffuse interstellargas with a temperature of tens of millions of degrees Celsiusis indeed the answer, other questions arise.What heats the gas to these incredible temperatures?Why does this energetic gas linger in the galactic plane?

A Piece of Interplanetary Dust

The dust that pervades our Solar System is not the dust that pervades our homes. Solar System dust comes from comets and asteroids, whereas house dust is most likely lint or dead cells. Pictured above is a piece of interplanetary dust caught by a high-flying U2-type aircraft. It likely originates in the early days of our Solar System, being stored and later ejected by a passing comet. The particle is composed of glass, carbon, and a conglomeration of silicate mineral grains. It measures only 10 microns across, a tenth the width of a typical human hair. NASA's STARDUST mission, launched in 1999, is scheduled to pass through the tail of Comet Wild 2 in 2004 and return many more interstellar dust samples to Earth in 2006.

Eagle EGGs in M16

Star forming regions known as "EGGs" are uncovered at the end of this gian pillar of gas and dustin the Eagle Nebula M16). EGGs, short forevaporating gaseous globules,are dense regions of mostly molecula hydrogengas that fragment and gravitationally collapse to form stars.Light from the hottest and brightest of these new stars heats the end ofthe pillar and causes further evaporation of gas - revealing yet more EGGs and more young stars. Thispicture was taken by the Wide Field and Planetary Camera on board the Hubble Space Telescope.

A Mystery in Gamma Rays

Gammarays are the most energetic form of light, packing a millionor more times the energy of visible light photons.If you could see gamma rays, the familia skyscape of steady stars woul be replaced by some of themost bizarre object knownto modern astrophysics -- andsome which are unknown.When the EGRET instrument on the orbitin Compton Gamma-ray Observatory surveyedthe sky in the 1990s, it cataloged 27 celestialsources of high-energy gamma-rays.Researchers identified somewith exotic black holes neutron stars, and distan flaring galaxies.But 170 of the cataloged sources, shownin the above all-sky map, remain unidentified Many sources in this gamma-ray mystery map likelybelong to already known classes of gamma-ray emitters and are simply obscured or too faint to be otherwise positively identified.However, astronomer have called attention to the ribbonof sources winding through the plane of thegalaxy, projected here along the middle of the map, whichmay represent a larg unknownclass of galactic gamma-ray emitters.In any event, the unidentified sources could remain a mysteryuntil the planned launch of the more sensitiv Gamma-ray LargeArea Space Telescope in 2005.

Perseids of Summer

Like fallin stardust,cast off bits of cometSwift-Tuttle hurtle throughthe upper atmosphere about this time each year as planet Earth passesnear the comet's orbital path.For the northern hemisphere, thi regularcelestial display is known as the annua Perseidmeteor shower -- so named because the meteor trailsall appear traceable to a common "radiant point" in th constellation Perseus.This gorgeous wide-angl photo from the 1997 showe captures a20-degree-lon fireball meteorand another, fainter Perseidmeteor trail in a rich area of the norther summer Milky Way.A labeled versio is available identifyingthe shower's radiant point,surrounding deep-sky objects, and constellations Easy to view (just go outside and look up!), thePerseid meteorshower will peak this weekend with maximum rates anticipatedearly Sunday morning, August 12, for eastern North America.Despite interfering moonlight last year's faithfu Perseid watcherswere rewarded with bright meteors and extensive displays o thenorthern lights.

Tycho and Copernicus Lunar Ray Craters

Dazzling in binoculars or a small telescope, the Moon ispocked with impact craters.During partia lunarphases, the craters along the terminatorare cast in dramatic relief by strong shadows.But when the Moon is full some craters seem to sprout systemsof bright radial lines or rays This detailed digital close-upof the full Moon features tw prominent ray craters,Copernicus (upper left) and Tycho (lower right), each with extensive ray systems of light colored debris blasted outby the crater-forming impacts.In general, ray craters are relatively young as their rays overlaythe lunar terrain.In fact, at 85 kilometers wide, Tycho, with its far reaching rays,is the youngest large crater on the nearside Crater Copernicus, surrounded by dark mare which contrastnicely with its bright rays, is 93 kilometers in diameter.

Farewell Jupiter

Next stop: Saturn. The Cassini spacecraft, launched from Earth four years ago, has now swung past Jupiter and should arrive at Saturn in the year 2004. Pictured to the left is a parting shot from Cassini in January that would not have been possible from Earth: Jupiter showing a crescent phase. From the Earth and all points sunward of Jupiter, the gas giant will always appear more fully lit than a crescent. After arriving at Saturn, Cassini will decelerate to orbit the ringed world and send a probe to its enigmatic moon Titan.

A July Dawn

Those up before dawn in late July in the northern hemisphere could see planets, stars, and a spacecraft in a single quick glance before starting their day. Near the eastern horizon was bright Jupiter, and not far above and to its right was the very bright Venus. Connecting the dots will point you just right of Saturn. Far in the distance but near the top right of the frame is the Pleiades star cluster. Orbiting the Earth well in the foreground, the International Space Station reflected sunlight to cause the faint line segment. In the very close foreground, the bright red and yellow lines were caused by a passing van. The above picture was taken on July 26 from Quebec, Canada. Why are bushes visible through the van? The van was present for only a few of the 25 seconds of the total exposure.

The Orbiting Hubble Space Telescope

The Hubble Space Telescope (HST) is the largest orbiting public optical telescope in history. Its 2.4 meter diameter reflecting mirror and its perch above Earth's atmosphere allow it to create exceptionallysharp images. Originally launched in 1990, HST optics were repaired to their intended accuracy in 1993 by the first of several regular servicing missions. Astronomers using HST continue to make numerous monumental scientific discoveries, including new estimates of the age and composition of our universe, previously unknown galaxies, evidence of massive black holes in the centers of galaxies, protoplanetary star systems and star forming regions,and a better understanding of physical processes in our universe.A larger Next Generation Space Telescope (NGST) may be launched as early as 2007.

NGC 2440 Cocoon of a New White Dwarf

Like a butterfly, a white dwarf star begins its lifeby casting off a cocoon that enclosed its former self. In this analogy, however, the Sun would be a caterpillar and the ejected shell of gas would become the prettiest of all!The above cocoon, the planetary nebula designated NGC 2440, contains one of the hottest white dwarf stars known.The white dwarf can be seen as the bright dot near the photo's center. Our Sun will eventually become a "white dwarf butterfly",but not for another 5 billion years. The above false color image and was post-processed by Forrest Hamilton.

Neighboring Galaxy The Large Magellanic Cloud

The brightest galaxy visible from our own Milky Way Galaxy is the Large Magellanic Cloud (LMC). Visible predominantly from Earth's Southern Hemisphere, the LMC is the second closest galaxy, neighbor to the Small Magellanic Cloud, and one of eleven known dwarf galaxies that orbit our Milky Way Galaxy. The LMC is an irregular galaxy composed of a bar of older red stars, clouds of younger blue stars, and a bright red star forming region visible near the top of the above image called the Tarantula Nebula. The brightest supernova of modern times, SN1987A, occurred in the LMC.

Warped Spiral Galaxy ESO 510 13

How did spiral galaxy ESO 510-13 get bent out of shape? The disks of many spirals are thin and flat, but not solid. Spiral disks are loose conglomerations of billions of stars and diffuse gas all gravitationally orbiting a galaxy center. A flat disk is thought to be created by sticky collisions of large gas clouds early in the galaxy's formation. Warped disks are not uncommon, though, and even our own Milky Way Galaxy is thought to have a small warp. The causes of spiral warps are still being investigated, but some warps are thought to result from interactions or even collisions between galaxies. ESO 510-13, pictured above, is about 150 million light years away and about 100,000 light years across.

Burning Tree Sprite

This dramatic, garishly colored image was captured with a low-light levelcamera on 2001 June 7.It shows what appears to be a "burning tree" above the NationalCheng Kung University campus in Tainan City, Taiwan ...but the burning tree is actually fleetingred sprite 300 kilometers away Redsprites ar recently discoveredand still poorly understood optical flashes seen dancingat altitudes of 30 to 90 kilometersabove thunderstorms Cousins t lightning bolts,red sprites occur near the edgeof the atmosphere and have been glimpsed by astronaut from orbit.What ever their cause the red sprite flashes usually last onlytenths to hundredths of a second and characteristically take on shapeswhich researchers describe as columns, fingers, trees, or carrots.

Young Martian Terrain

What caused the pits, ridges, and gullies on otherwise smooth Martian terrain? One hypothesis is water. The lack of craters at this mid-latitude location indicates that the terrain is quite young by geological standards, perhaps only 100,000 years old. Were the terrain since saturated by water ice, that ice would soon evaporate into the thin Martian air. Left over, however, might be fragile cake-like sand that can be broken up by wind into pits and ridges. Consequences of this hypothesis include that even the Martian equator undergoes epochs of relative wet and dry, and that future spacefarers might be able to find water (ice) in a relatively mild climate near the Martian equator Pictured above is young-ridged terrain that also shows evidence of a downhill flow.

Oceans Under Jupiters Callisto

Why does Jupiter's moon Callisto alter the magnetic field of Jupiter in its vicinity? Callisto itself does not have a strong magnetic field. One possible answer is that Callisto harbors sub-surface oceans of electrically conducting salt-water. This hypothesis was bolstered recently by a new analysis of how Callisto creates and dissipates heat. Callisto is thought to create heat by the radioactive decay of internal rock -- a process that keeps the Earth's mantle molten. Callisto may not be able to dissipate this heat very efficiently, however, as it has thick layers of ice and rock on its surface. Perhaps this heat is enough to keep sub-surface water from freezing into ice. With this hypothesis, Callisto joins two other of Jupiter's moons, Europa and Ganymede, in candidates for sub-surface oceans. Callisto's oceans, however, might prove too hostile to support Earth-like life.

Star Cluster R136 Bursts Out

In the center of star-forming region 30 Doradus lies a huge cluster of the largest, hottest, most massive stars known.Known as R136, the cluster's energetic stars are breaking out of thecocoon of gas and dust from which they formed.This disintegrating cocoon, which fills the rest of the recently released above picture by the Hubble Space Telescope, is predominantly ionized hydrogen from 30 Doradus R136 is composed of thousands of hot blue stars, some about 50 times more massive than our Sun. R136, also known as NGC 2070, lies in the LMC - a satellite galaxy to our own Milky Way Galaxy. Although the young ages of stars in R136 make it similar to a Milky Way open cluster, its high density of stars will likely turn it into a low mass globular cluster in a few billion years.

M57 The Ring Nebula

Except for the rings of Saturn, th Ring Nebula (M57) is probably the most famous celestial band.Thi planetary nebula's simple, gracefulappearance is thought to be due to perspective --our view from planet Earthlooking straight into what is actually a barrel-shaped cloud ofgas shrugged off by a dying central star.Astronomers of the Hubble Heritage Project produce this strikingly sharp image from Hubble Space Telescope observations using natural appearing colors to indicate the temperature of the stellar gas shroud.Hot blue gas near the energizing central stargives way to progressively cooler green and yellowgas at greater distances with the coolest red gas along the outer boundary Dark, elongated structurescan also be seen near the nebula's edge The Ring Nebula is about one light-year across and 2,000 light-years away in the norther constellation Lyra.

A Daytime Fireball in 1944

While stationed in central Africa in December 1944, Norman Appleton witnessed a meteor so bright he remembered it his entire life. Right before his eyes a tremendous smoking fireball streaked across the daytime sky. Years later, as an accomplished member of the Guild of Aviation Artists, he recorded his memories in the above painting. Several days ago, on July 23 at 6:19 pm EDT, a daytime fireball visible from the northeast United States was reported by many personal accounts. No pictures of this event have yet surfaced, although it is quite possible that a video security camera somewhere caught it serendipitously.The bolide was likely caused by a sofa-sized rocky meteor disintegrating as it fell to Earth, an event that occurs over some unpopulated area almost every day.

Martian Dust Storm

If you've been unhappy with the weather on Earth checkout Mars, now in the grip of planet-wide dust storm.Above, observations fro the orbitingMars Global Surveyor (MGS)spacecraft illustrate the storm's progress through July 21.The series of dated frames show measurements from the MG Thermal Emission Spectrometerwhich can determine both temperature and amount ofatmospheric dust.Dust dat hasbeen plotted on maps of the martian surface with bluerepresenting relatively clear atmosphere and red colors indicatingincreasing concentrations of dust.In mid June, scientists first noticed the beginnings of the storm i Mars'southern hemisphere and have watched it grow to obscure most ofthe planet.Unfortunately fo Mars-watchers,the timing of the storm has hidde theRed Planet's surface from view during its period ofclose approach to planet Earth.

Madagascar Totality

When the Moon's shadow reached out and touched Earth's southernhemisphere on 2001 June 21, the firs totalsolar eclipse of the 21st century began.Starting in the Atlantic, the dark, central lunar shadow or umbratraced a path which crossed southern Africa and the large islan ofMadagascar before ending at sunset in the Indian Ocean.Of course, as the lunar dis blocked the Sun the total phase offeredsplendid views of the elusive outer solar corona.But, as seen in this stunning telescopic view from southernMadagascar, it also revealed a active solar limb bristling withpinkish, planet-sized prominences Taken as totality began, this image of the last bright rays ofsunlight shining through dips and valleys in irregular lunarterrain gives the illusion of glittering jewel set in a pink celestialring.

Hot Gas Halo Detected Around Galaxy NGC 4631

Is our Milky Way Galaxy surrounded by a halo of hot gas? A step toward solving this long-standing mystery was taken recently with Chandra X-ray observations of nearby galaxy NGC 4631. In the above composite picture, newly resolved diffuse X-ray emission is shown in blue, superposed on a HST image showing massive stars in red. Since NGC 4631 is similar to the Milky Way, this observation indicates that our own Galaxy is indeed surrounded by a halo of hot X-ray emitting gas, although we are too close to clearly differentiate it from more nearby extended X-ray sources. The clusters of massive stars probably heat the halo gas. Exactly how this gas gets ejected into a halo is a topic of continuing research.

The Red Spider Planetary Nebula

Oh what a tangled web a planetary nebula can weave. The Red Spider Planetary Nebula shows the complex structure that can result when a normal star ejects its outer gases and becomes a white dwarf star. Officially tagged NGC 6537, this two-lobed symmetric planetary nebula houses one of the hottest white dwarfs ever observed, probably as part of binary star system. Internal winds emanating from the central stars, visible in the center,have been measured in excess of 1000 kilometers per second. These winds expand thenebula, flow along the nebula's walls, and cause waves of hot gas and dust to collide. Atoms caught in these colliding shocks radiate light shown in the above representative-color picture. The Red Spider Nebula lies toward the constellation of Sagittarius. It's distance is not well known but estimated by some to be about 4000 light-years.

Wednesday, 25 June 2008

Atlantis to Orbit

Birds don't fly this high. Airplanes don't go this fast. The Statue of Liberty weighs less. No species other than human can even comprehend what is going on, nor could any human just a millennium ago. The launch of a rocket bound for space is an event that inspires awe and challenges description. Pictured above, the Space Shuttle Atlantis lifted off to visit the International Space Station during the early morning hours of July 12. From a standing start, the two million kilogram rocket ship left to circle the Earth where the outside air is too thin to breathe and where there is little noticeable onboard gravity. Rockets bound for space are now launched from somewhere on Earth about once a week.

NGC 1977 Blue Reflection Nebula in Orion

The Orion Nebula is visible to the unaided eye as a fuzzy patch near the famou belt of three stars in the Orion. The above picture captures a part of the Orion Nebula that primarily reflects light from bright Orion stars. This reflection nebula appears blue because the blue light from the neighboring stars scatters more efficiently from nebula gas than does red light. The dark lanes are composed of mostly interstellar dust - fine needle-shape carbon grains.

25 Years Ago Vikings on Mars

OnJuly 20, 1976, NASA's Viking 1 lander becam thefirst U.S. spacecraf to land on Mars,followed weeks later by its twin robotexplorer, the Viking 2 lander Operating o the Martian surfaceinto the early 1980s theVikings took thousands of pictures conductedsophisticated chemica searches for life,and studied th martian weatherand geology.In the dramatically detailed image above, a field of rocks and bouldersis viewed from the Viking 1 landing site on Chryse Planitia(the Plain of Chryse).Viking 1's dusty foot pad is just visible at the lower right The image was createdby combining high resolution black and white imageswith lower resolution color images of the same area.NASA is continuing it wellchronicled martian exploration program asthe Mars Odysseyspacecraft is scheduled to arriveat the mysterious Red Planet on October 24th.What's Mars like today?

The Elephant's Trunk in IC 1396

Like a picture from a galacti JustSo Story, th Elephant's Trunk Nebulawinds through the emission nebula and young star cluste complexIC 1396, in the high and far off constellatio of Cepheus.Bright swept-back ridgescompose the suggestive form, outlining pockets of interstellar dustand gas.Such embedded dark comet-shaped clouds contain theraw material for star formation.About 3,00 light-years distant, the relatively fain IC1396 complex covers a much larger region on the sky than shownhere, with an apparent width of more than 10 full moons Thisclose-up telescopic view is a delightfu colormosaic of two digital images intended to followthe 'satiablecurious cosmic trunk.

Pulsar Wind in the Vela Nebula

The Vela pulsar was born10,000 years ago at the center ofa supernova -- a exploding star.In this Chandra Observator x-ray image, the pulsar still produces aglowing nebula at the heart of the expanding cloud ofstellar debris The pulsaritself is neutron star,formed as the stellar cor was compacted to nuclear densities.With a strong magnetic field, approximately the mass of the Sun,and a diameter of about 20 kilometers, the Vela pulsar rotates11 times a second.The sharp Chandra imag aids astronomersin understandingsuch extreme systems as efficien high-voltagegeneratorswhich drive structured windsof electrically charged particles.An x-ray bright nebula is created as the pulsar windsslam into the surrounding material.This view spans about 6 light-years across the central region of themuch larger Vela supernova remnant.

Mars from Earth

Last month, Mars and Earth were right next to each other in their orbits. Formally called opposition, the event was highlighted by a very bright Mars for skywatchers and a good photo opportunity for the Hubble Space Telescope. Above, Hubble snapped the highest resolution picture of Mars ever obtained from the Earth. Visible on Mars are ice caps over the poles in white, regions covered with sand and gravel in dark brown and orange, and large dust storms in light orange. A particularly large dust storm can be seen on the lower right pouring out of Hellas Basin. This storm has since erupted into a huge planet wide storm that continues even today.Pictures like these allow planetary astronomers to continue to compare the weather patterns of Mars and Earth. When Mars next reaches opposition in 2003, its elliptical orbit will cause it to be even 20 percent closer.

The Carina Nebula in Three Colors

Stars, like people, do not always go gentle into that good night. The above Carina Nebula, also known as the Keyhole Nebula and NGC 3372, results from dying star Eta Carinae's violently casting off dust and gas during its final centuries. Eta Carinae, one of the most luminous stars known, is visible as the bright star near the center of the nebula. The above picture was taken in three distinct colors of light: blue light as emitted from hot oxygen, green light as emitted by warm hydrogen, and red light as emitted by cool sulfur. Eta Carinae faded from being one of the brightest stars in the sky during the 1800s, but is still visible with binoculars in southern skies towards the constellation of Carina.

Water Found Around Nearby Star CW Leonis

Do worlds outside our Solar System have oceans of water like Earth? An indication that such worlds might exist was bolstered recently by new evidence that nearby star system CW Leonis harbors water. Recent observations with the Submillimeter Wave Astronomy Satellite (SWAS) found significant detections of light at specific colors emitted by water. A hypothesis quickly arose that the activity of the central star is vaporizing water from a cloud of comets that surrounds the star -- a cloud that may be similar to the Kuiper Belt of comets that surrounds our own Sun. The above drawing depicts the CW Leonis system with its hypothesized cloud of water-bearing comets situated to a ring. The closest comets are depicted as showing tails rich in water vapor pointing away from the star. Far from the central star, however, comets should not show significant tails and should be more sparsely spaced. The central star, also known as IRC+10216, is an aging giant star located about 500 light-years away toward the constellation of Leo.

Io in True Color

The strangest moon in the Solar System is bright yellow. This picture, showing Io's true colors, was taken in 1999 July by the Galileo spacecraft currently orbiting Jupiter. Io's colors derive from sulfur and molten silicate rock. The unusual surface of Io is kept very young by its system of active volcanoes. The intense tidal gravity of Jupiter stretches Io and damps wobbles caused by Jupiter's other Galilean moons. The resulting friction greatly heats Io's interior, causing molten rock to explode through the surface. Io's volcanoes are so active that they are effectively turning the whole moon inside out. Some of Io's volcanic lava is so hot it glows in the dark.

Solar System Web Cam

Ranging throughout th solar system, these pictures allhave something in common.They were taken with an 8 inch diameter telescope, a size popularwith amateur astronomy buffs, and slightly modified "web cam"of the type widely used to send images out over the internet.The results are clearl remarkablefor such inexpensive and readily available equipment.Each sharp image was produced from 20 to 30 frames whichwere digitally stacked and processed usin free software.Until recently, digital imaging for amateur astronomers required specialized camera,but the advent of low-lightvideo surveillance cameras and web cams now presents otheroptions fo relativelybright solar system objects.Want to try som unconventionalweb cam astronomy?Geoff Chester, Public Affairs Officer at th U.S. Naval Observatory,offers these images and a accountof his own adventuresfrom a suburban front lawn near Washington D.C.

Welcome to the Moon Hotel

The most detailed proposalso far for a hotel and resort destinatio on the Moon (!) has been prepared b Dutcharchitect Hans-Jurgen Rombaut. The hars lunar environmentposed seriou design challenges but the Moon's low one-sixth-Earth gravity,and the absence of wind were anarchitectural boon allowing a much more slender and fragile-lookingbuilding than would have bee possible on Earth.Illustrated here, the structure's two 160 meter high needle-lik towers soar overthe rim of a deep canyon as planet Earth hangs in th lunar sky.To shield the interior, Rombaut designed 50 centimeter thick wallswith two outer layers of Moon rock and a 35centimeter layer o waterheld between glass planes.The water absorbs energetic cosmic rays and along with therock helps keep the temperature constant.Windows are framed as holes in the rock layers Constructionmaterials are intended to be manufacture on the Moon itself.This Moon Hotel design is welcomed by the international LunarExplorers Society, LUNEX,who hope to construct a roboti Moon base by 2015 ultimatelysupporting a lunar village by 2040.

NGC 1850 Not Found in the Milky Way

A mere 168,000 light-years distant, this large, lovely cluster ofstars, NGC 1850,is located near the outskirts of the centralbar structure in our neighboring galaxy, th LargeMagellanic Cloud.A first glanc atthis Hubble Space Telescop compositeimage suggests thatthis cluster's size and shape are reminiscent of the ancient globularstar clusters which roam our ow Milky Way Galaxy's halo.But NGC 1850's stars are young ... making it a typ of star clusterwith no known counterpar in the Milky Way.NGC 1850 is also a double star cluster, with a second, compactcluster of stars visible here below and to the right ofthe large cluster's central region.Stars in the large cluster are estimated to be50 millio yearsyoung, while stars in the compact cluster areyounger still, with an age of about 4 million years.In fact, the smaller cluste contains T-Tauristars, thoughtto be low mass, solar-type stars stil in theprocess of formation.The glowing nebula at the left, like th supernova remnants in our own galaxy testifies to violent stellar explosions,indicating short-lived massive starswere also presen in NGC 1850.

A Total Eclipse Over Africa

What's that dark spot on the Sun? It's the Moon. Last month, on June 21, a total solar eclipse was visible in parts of Africa. In one of the most spectacular records of this eclipse, Cees Bassa captured the setting Sun being eclipsed in a series of multiple exposures from Malambanyama, Zambia. All of the images were taken 20 minutes apart, and all but the central image were taken though a dark solar filter. Without the filter, the central image features the enormous flowing corona that surrounds the Sun.The planet Jupiter can be seen superposed just to the left of the next image after totality.

Sudbury Indicates Nonstandard Particle Model

The Sudbury Neutrino Observatory (SNO) has been detecting so few neutrinos from the Sun that the Standard Model of fundamental particles in the universe may have to be revised. Pictured above is the SNO as it was being built. Now operating, this large sphere beneath Canada is detecting nearly invisible particles called neutrinos being emitted from the center of the Sun. SNO appears to be measuring a rate expected for all types of neutrinos combined but a decided deficit for the electron neutrino. The results are being interpreted as bolstering previous evidence that different types of neutrinos are changing into each other. The most popular model for fundamental particles, known as the Standard Model, did not predict such schizophrenic neutrinos. Implications include that neutrinos have mass and therefore comprise some of the dark matter in the universe, although probably not a cosmologically significant amount.

Air Pollution Earth

Where on Earth is the air most polluted? Recently released images from the Terra satellite show not only areas of high pollution, but also how polluted air moves. In the above image, locations of higher air pollution are shown in red. The pollutant tracked is carbon monoxide (CO) at a height of about 5 kilometers. Clearly, Earth's Northern Hemisphere shows much more CO than the south. The new data indicate, however, that pollution moves on a global scale. About half of all CO emission is of human origin, and much of this is created in large fires.

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 above photograph. The Galactic Center itself appears on the right and is located about 30,000 light years away towards the constellation of 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.

A Close Encounter Of The Stellar Kind

The unassuming star centered in thi sky view will one day be ou next door stellar neighbor.The faint 9th magnitude red dwarf,currently 63 light-years away i theconstellation Ophiucus, was recently discoveredto be approaching our Solar System.Known in catalog of nearbystars as Gliese (Gl) 710 it ispredicted to come within nearly 1 light-year of the Sun ...about 1.5 million years from now.At that distance this star, presently muc toofaint to be seen by thenaked eye, will blaze at 0.6 magnitude - rivaling the apparentbrightness of the mighty red giant Antares.Ultimately Gliese 710 posesno direct collision danger itself although itsgravitational influence will likely scatter comets out ofthe Solar System's reservoir the Oort cloud, sending some inbound This future stellar encounter wasdiscovered by researchersJoan Garcia-Sanchez and Robert Preston JPL), and collaborators while studyin stars in the solar neighborhoodusing data fro the Hipparcos Astrometry Satellite.The star field shown is based on th PalomarDigitized Sky Survey andis 1/4 degree wide (about half the diameter of the full moon).

Bakasa Eclipse Sequence

Starting at the upper left, this sequence of images followsthe progress of the magnificent 21 June 2001solar eclipse in the clear skies over Bakasa, Zimbabwe.These pictures were recorded using a smal reflecting telescope an digitalcamera with the approximate local time given above each frame.A simple pair of "eclipse spectacles" were mounte as a filterin front of the telescope mirror and removed durin totality.In the early and late phases of this eclipse o theactive Sun, sunspot groups can be seen lingering on th solar surface Duringeclipse totality, pinkish prominences are visible at thesolar limb along with details of the normall hiddensolar corona.Seen from thi location, the total eclipsephase lasted just under 3 1/2 minutes as th Moon's shadow rushedacross northern Zimbabwe at nearly 5,000 kilometers per hour.

C/2001 A2 (LINEAR) Comet !

CometC/2001 A2 (LINEAR) has crossed the celestial equator and isheading north Outward bound,this primordialpiece of the solar system is stilljust visible to the unaided eye and can now be sighted by northernhemisphere skygazers as it move throughthe constellation Pisces Thispicture of the comet is a combination of 33 individual one minuteexposures made on June 30 with a small telescope anddigital camera situated in central Arizona, USA.The composite image brings out faint detailsin the comet's tail whic wasreported to extend for several degrees,beyond the camera's roughly 2 degree field of view.Closely spaced, the combined exposures were registered on thecomet so background stars appear trailed.To produce the "punctuation" at the end of eac star trail, two exposuresnear the end of the sequence were left out.As a result, the final dots nicely reveal the pattern of thebackground star field.

Moonbow with Sailboats

Have you ever seen a moonbow? Just as rainbows are lit by the Sun, moonbows are lit by the Moon. Since the Sun is so much brighter than the Moon, sunlit rainbows are much brighter and more commonly seen than moonbows. Pictured above is a moonbow stretching over Salt Pond Bay in St. John, Virgin Islands. Sailboats are visible on the left. To bring out the moonbow, an exposure of 30 seconds was needed, making the picture appear as if it was taken during the day. Since moonlight is itself reflected sunlight, the colors are nearly the same.Both rainbows and moonbows are created by light being scattered inside small water droplets, typically from a nearby rainfall. The raindrops each act as miniature prisms, together creating the picturesque spectrum of colors seen.

Unusual Flashes Toward Globular Cluster M22

What is causing the unusual flashes behind globular cluster M22? This teeming ball of stars is the brightest globular cluster visible from Earth's northern hemisphere. M22, shown in full in the inset, spans about 50 light-years and lies 8,500 light-years away toward the constellation of Sagittarius. M22's center was recently imaged repeatedly by the high resolution Hubble Space Telescope. Behind M22 are many more stars near the center of our Galaxy. Unexpectedly, several stars near the Galactic center -- well behind M22 -- appeared to nearly double in brightness and return to normal within 20 hours. One hypothesis posed to explain these quick brightness changes is the gravitational lens effect of large planets roaming freely in the cluster. One problem with this is that no suc planetary population was previously known! Future observations are planned to better understand these mysterious flashes.

The Seasons of Saturn

Soon it will be winter in Saturn's northern hemisphere. Since Saturn is tilted in its orbit around the Sun, it has seasons just like the Earth. When a hemisphere is tilted so that the Sun passes more directly overhead, summer occurs. Half an orbit later -- about 15 (Earth) years for Saturn -- winter occurs. Since the rings of Saturn orbit the equator, they provide a quite graphic seasonal display. The Hubble Space Telescope took the above sequence of images about a year apart, starting on the lower left in 1996. Saturn's rings are less than 50 meters thick and are composed of pebble and boulder sized chunks of dusty water ice.

Spiral Galaxy NGC 7742

This might resemble a fried egg you've ha for breakfast, but it'sactually much larger.In fact, ringed by blue-tinte star forming regions andfaintly visible spiral arms,the yolk-yellow center of this face-on spiral galaxy, NGC 7742, is about 3,000 light-years across.About 72 million light-years away in the constellation Pegasus,NGC 7742 is known to b a Seyfert galaxy - a type o active spiral galaxy with a center or nucleus which is very brigh at visible wavelengths.Across the spectrum,the tremendous brightness of Seyferts can change over periods ofjust days to months and galaxies like NGC 7742 aresuspected of harborin massive black holes at their cores.This beautiful color picture is courtesy of the Hubble Space Telescope Heritage Project.

Hydrogen, Helium, and the Stars of M10

Stars like the Sun use hydrogen for fuel,"burning" hydrogen into helium at their core through nuclear fusion.But what happens when that hydrogen runs out?For a while, hydrogen burns in a shell surrounding the stellar coreand the star expands to become a red giant.The bright reddish-orange stars i thisbeautiful two-color compositepicture of the ol globularstar cluster M10 are examples of this phas ofstellar evolution.Yet the bright blue stars apparent in M10 have evolved beyondthe simple, hydrogen shell burning stage.These stars have become "horizontal branch" giants withcore temperatures hot enough to burn helium into carbon.In this image, only the barely visible, faint, gray-lookin stars are likely to still be burninghydrogen at their cores.

Ice Volcanoes on Mars

What causes these unusual cone-shaped features on Mars? Spanning an average of only 100 meters at the base, these small cones appear near massive Martian volcanoes such as Olympus Mons. Near the cones are also dry channels and eroded banks. Given these clues, some scientists speculate that the cones were formed by lava heating ice lying just below the Martian surface. Lava heated ice would vaporize and expand, punching holes in the cooling lava flow as it escaped. Interestingly, nearby volcanoes may have erupted as recently as 10 million years ago, indicating the equatorial near-ground ice existed in the recent past, and therefore may also exist there today.

The Topography of Mars

APOD: 2001 June 28 - The Topography of Mars

Moonlight, Mars and Milky Way

Alohaand welcome to a breath-taking skyscape.In this celestial scene,a four day old Moon illuminates a dreamlike foreground whil bright planet Mars(above center) rules an theMilky Way's cosmic clouds of stars and dust seem to stretchfrom horizon to horizon.The picture was taken on May 27th from what may be the bestamateur astronomy observing sit on planet Earth, near th Mauna Kea, Hawai'iVisitor Center, 9,600 feet above sea level.Remarkable in the volcanic foreground are moonlit clouds andan "ahu hoku" - a star marker or star altar - built up of rockstopped with a white piece of coral gently glowing in the moonlight.Now near its closest approach in 13 years Mars still lingers between th Milky Way constellations ofSagittarius and Scorpius.High above the horizon by midnight the Red Planet isexceptionally well placed fo earthdwellers to admire it.Astrophotographe Barney Magrathcomments that this splendid sky viewrepresents one of the joys o photography itself.When making the time exposure he did not realize that theahu hoku would become such a beautiful element in his celestialcomposition.

All of Mars

From pole to pole, from east to west, this is all of Mars. The above picture was digitally reconstructed from over 200 million laser altimeter measurements taken by the Mars Global Surveyor spacecraft currently orbiting Mars. The image strips Mars of its clouds and dust, and renders the whole surface visible simultaneously in its true daytime color. Particularly notable are the volcanoes of the Tharsis province, visible on the left, which are taller than any mountains on Earth. Just to the left of center is Valles Marineris, a canyon much longer and deeper Earth's Grand Canyon. On the right, south of the center, is the Hellas Planitia, a basin over 2000 kilometers wide that was likely created by a collision with an asteroid. Mars has many smooth lowlands in the north, and many rough highlands in the south Mars has just passed its closest approachto Earth since 1988 and can be seen shining brightly in the evening sky.

A Brighter Comet LINEAR

Brighter than eve expected, comet LINEAR - you know, the one designate C/2001 A2 -- is a sight to seein southern skies This comet LINEAR first brightenedimpressively in late March as its active nucleus bega to fragment, prompting somespeculation that the comet might soo break up completely.But still hanging together after its closest approach tothe Sun, C/2001 A2 suddenly brightened again an was reportedlast week to have reached nearly 3rd magnitude,easily visible to the unaided eye Thisdelightful telescopic picture of the brightercoma of comet LINEAR was recorded from Australia on June 20.Stars seen through the tenuous comaand filamentary tail appear as a series of short trails inthis three-color composite image registere on the comet.North is up and the scene covers about half the width ofthe full Moon.Now moving through th constellation Cetus, comet LINEAR will benorth of the celestial equator by July 4 as itcomes into view for eager northern sky-gazers.

NGC 3132 The Eight Burst Nebula

It's the dim star, not the bright one, near the center of NGC 3132 that created this odd but beautiful planetary nebula. Nicknamed the Eight-Burst Nebula and the Southern Ring Nebula, the glowing gas originated in the outer layers of a star like our Sun. In this representative color picture, the hot blue pool of light seen surrounding this binary system is energized by the hot surface of the faint star. Although photographed to explore unusual symmetries, it's the asymmetries that help make this planetary nebula so intriguing. Neither the unusual shape of the surrounding cooler shell nor the structure and placements of the cool filamentary dust lanes running across NGC 3132 are well understood.

Tuesday, 24 June 2008

The Cygnus Loop

The shockwave from a 20,000 year-ol supernova explosionin the constellation of Cygnusis still expanding into interstellar space.The collision of this fast moving wall of gas with a stationary cloud has heated it causing it toglow in visible as well a high energy radiation, producing the nebula known as th Cygnus Loop (NGC 6960/95).The nebula is located a mere 1,400 light-yearsaway.The colors used here indicate emission from different kinds of atoms excited by the shock: oxygen-blue, sulfur-red, and hydrogen-green This picture was taken wit the Wide Field and Planetary Camera 2 on board the Hubble Space Telescope.

Eclipse in African Skies

Yesterday, for a brief few minutes, a tota eclipse of the Sunbrought darkness t southernAfrica's daytime skies.During this first total solar eclipse of the thir millenniumwebcast sites were swamped, but sun-watchers along the eclipse path enjoye clearweather and reported fantastic views.Enthusiastic astrophotographer Olivier Staige recorded these picturesduring the eclipse's total phase from Lusaka, Zambia.The large image above shows the Sun's tantalizing inner corona withtelltale pinkish prominences around the solar limb, while the inset atthe lower right reveals the spiky outercorona.But the inset also captures anothe celestial beacon sharing th eclipse-darkened heavens,the bright planet Jupiter shining at the lower left.The next total solar eclipse will be o 2002 December 4 ...again in southern African skies.

Diamond Ring in the Sun

Today, earthbound skygazers can celebrat a solstice a new Moon the closest approachof planet Mars since 1988 ... oh yes, and a total eclipse of the Sun, th firsttotal solar eclipse of the third millennium.Of course for some, today's most spectacular celestial views will be o theeclipsed Sunfrom along the path of totality as the new Moon'sshadow tracks across souther Africaand Madagascar.This picture from the August 1999 total solar eclipse captures theshimmering solar corona just as that eclipse's total phaseended, as seen from eastern Turkey.The first rays of bright sunlight shinnin through edge-onlunar mountains and valleyscreate the fleeting appearance of glistening diamonds set in aring around the Moon's silhouette.Do youwant to see today's solar eclipse?Eclipse expeditions are offerin live webcasts.

Total Eclipse of the Active Sun

totaleclipse of the Sun is that specia geocentriccelestial event where the Moon passes exactlyin front of the solar disk.During a fleetingfew minutes of totality, fortunate earthdwellers locatedwithin the path of the Moon's dark shado can witnessthe wondrous shimmering solar corona sharingthe sky with stars and bright planets.The next total solar eclipse will occu tomorrow, June 21.Since the Sun is stil near the maximumof its 11 year activity cycle carefuleclipse-watchers will also likely see the spectacle of bright solarprominences lofted above active regions around the Sun's edge.In fact, a telescopic view could be similar to this stunninglydetailed image -- a picture of the solar eclipse of August 1999taken at the beginning of totality from Kecel, Hungary.The upcomin 2001 June 21 eventwill be visible as a partial eclipsefrom some of South America and much of Africa,but will only be total along a125 mile wide path that tracks across landthrough Southern Africa and Madagascar.Of course, if you can't travel t Africatomorrow (and you're not already there) web sites planto offer live views from the Moon's shadow!

Crescent Neptune and Triton

Gliding silently through the outer Solar System, the Voyager 2 spacecraft camera captured Neptune and Triton together in crescent phase in 1989. The above picture of the gas giant planet and its cloudy moon was taken from behind just after closest approach. It could not have been taken from Earth because Neptune never shows a crescent phase to sunward Earth. The unusual vantage point also robs Neptune of its familiar blue hue, as sunlight seen from here is scattered forward, and so is reddened like the setting Sun. Neptune is smaller but more massive than Uranus, has several dark rings, and emits more light than it receives from the Sun.

NGC 4755 A Jewel Box of Stars

The great variety of star colors in this open cluster underlies its name: The Jewel Box. One of the bright central stars is a red supergiant,in contrast to the many blue stars that surround it. The cluster, also known as Kappa Crucis contains just over 100 stars, and is about 10 million years old. Open clusters are younger, contain few stars, and contain a much higher fraction of blue stars than do globular clusters. This Jewel Box lies about 7500 light-years away, so the light that we see today was emitted from the cluster before even the Great Pyramids in Egypt were built. The Jewel Box, pictured above, spans about 20 light-years, and can be seen with binoculars towards the southern constellation of Crux.

Colorful Clouds Of Carina

Tumultuous clouds o the Carina Nebula,8000 light-years away, glow in planet Earth' southern sky.Striking and detailed this close-up of a portion o the famous nebulais a combination of exposuresthrough six different filters taken with th Hubble Space Telescope's Wide Field PlanetaryCamera 2 in April of 1999.Dramatic dark dust knots and complex features revealed ar sculptedby the winds and radiation of Carina's massive an energetic stars.But how were this picture' colors generated?Astronomical images produce from Hubble Space Telescope datacan be composed of exposures made using relatively narrow filters which don't match the color responses of th human eye.Some of the filters even transmit wavelengths of light outsid the visible spectrum.Exposures made with different narrow filters as in this case,are translated to a visible color where shorter wavelengths are assignedbluer and longer wavelengths assigned redder colors.This color scheme represents a "chromatically ordered"way of presenting the data rather than natural color image.

is Six Years Old Today

Welcome to the seventh year o Astronomy Picture of the Day (APOD) EditorsRobert Nemiroff and Jerry Bonnell are extremelygrateful for the continued large volume ofgracious e-mail and APOD submissions (and also for the "occasional"critical note!) Todaywe would like to offer a very sincere thank you to all.We are certainly proud that each day over th last six yearsAPOD has consistently coupled an expanding universe o hypertext with inspirin images of the cosmos.In fact, tomorrow's picture might actually be ...

Messiers and Mars

A telescopic tour of th constellation Sagittarius offers the manybright clusters and nebulae o dimensioned space in starscapesurrounding th galactic center.This gorgeou colordeep-sky photograph visits two such lovely sights,cataloged by the 18th century cosmic touris CharlesMessier as M8 and M20.M20 (upper left) the Trifid Nebula, presents a striking contrast inred/blue colors and dark dust lanes.Just below and to the right is theexpansive, alluring red glow of M8 the Lagoon Nebula.Both nebulae are a few thousand light-years distantbut at the far right, the dominant celestial beacon is a "local"source theplanet Mars.Just passing through Sagittarius andstrongly overexposed in this picture the Red Planetis a short 4 light-minutes away Nownear its closest approach to planet Earth since 1988,Mars rises around sunset an can be seenfor most of the nigh shiningbrightly at about -2. magnitude Urban imagerMichael Cole recorded this photograph at 3:00 AM on May 20thin clear skies over Camp Hancock, Oregon, USA.