NASA Astronomy Picture of the Day 2003-1

NGC 6960: The Witch's Broom Nebula

Ten thousand years ago, before the dawn of recorded human history, a new light must suddenly have appeared in the night sky and faded after a few weeks. Today we know this light was an exploding star and record the colorful expanding cloud as the Veil Nebula. Pictured above is the west end of the Veil Nebula known technically as NGC 6960 but less formally as the Witch's Broom Nebula. The rampaging gas gains its colors by impacting and exciting existing nearby gas. The supernova remnant lies about 1400 light-years away towards the constellation of Cygnus. This Witch's Broom actually spans over three times the angular size of the full Moon. The bright blue star 52 Cygnus is visible with the unaided eye from a dark location but unrelated to the ancient supernova.

Mt. Etna Eruption Plume

Mt. Etna has been erupting for hundreds of thousands of years. In late October of last year, however, earthquakes triggered a particularly vigorous outburst from this well known volcano on the Italian island of Sicily. Local schools were closed and air-traffic re-routed as hot lava poured out and ash spewed out and settled as far away as Libya. Pictured above was the Mt. Etna ash plume as it appeared to astronauts on the International Space Station. The view looks toward the southeast. Light colored smoke is due to forest fires caused by lava on the volcano's north face.

POX 186: Not So Long Ago

Not so long ago and not so far, far away, a galaxy was born. Seen in this Hubble Space Telescope image, the island universe of stars, gas, and dust cataloged as POX 186 is a mere 68 million light-years distant toward an uncrowded region in the constellation Virgo. POX 186 is truly dwarfed by galaxies like our own Milky Way. The diminutive galaxy is about 900 light-years across with around 10 million stars, compared to the Milky Way's 100,000 light-year span and more than 200 billion stars. Cosmically speaking, POX 186 is also very young as the Hubble snapshot reveals a disturbed galaxy that is likely the result of a 100 million year old collision between two even smaller star systems. In fact, POX 186 observations suggest that such isolated, small galaxies may be the last to form, since the most massive galaxies in the universe seem to have formed billions of years ago.

A Magellanic Starfield

Stars of many types and colors are visible in this Hubble Space Telescope close-up of a starfield in the Large Magellanic Cloud (LMC). Over 10,000 stars are visible -- the brightest of which are giant stars. Were our Sun at the distance of these stars, about 170,000 light-years, it would hardly be discernable. By contrast, only a few thousand individual stars can be seen in the night sky with the unaided eye, and many of these lie within only a few hundred light-years. So typically, the light we see from nearby stars left during the age of our great-grand-parents, while light from LMC stars started its journey well before the dawn of recorded human history.

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.

Shadow Cone of a Total Solar Eclipse

Sometimes, during a total eclipse of the Sun, a strange shadow of darkness can be seen stretching off into the distance. Called a shadow cone, they are visible because the Earth's atmosphere is not completely transparent, scattering sunlight and hence appearing blue during the day. Shadow cones are particularly dramatic for eclipses near the horizon, as geometry creates a long corridor of sun-blocked air. Visible above is a shadow cone caught during a total solar eclipse visible last month from South Australia. The eclipsed Sun itself still appears bright because of light from the surrounding corona. The digital camera on the left is zoomed in to show a better image of the actual eclipse.

Open Star Cluster M38

Open cluster M38 can be seen with binoculars toward the constellation of Auriga. M38 is considered an intermediately rich open cluster of stars, each of which is about 200 million years old. Located in the disk of our Milky Way galaxy, M38 is still young enough to house many bright blue stars, although it's brightest star is a yellow giant shining 900 times brighter than our Sun. The cluster spans roughly 25 light-years and lies about 4000 light-years away. M38, pictured above, is found only about 2.5 degrees northwest of open cluster M36. Loosely bound by gravity, open clusters spread out over time as they orbit the galactic center and their member stars slowly escape.

X-Rays from the Galactic Core

Using the orbiting Chandra X-ray Observatory, astronomers have taken this long look at the core of our Milky Way galaxy, some 26,000 light-years away. The spectacular false-color view spans about 130 light-years. It reveals an energetic region rich in x-ray sources and high-lighted by the central source, Sagittarius A*, known to be a supermassive black hole with 3 million times the mass of the Sun. Given its tremendous mass, Sagittarius A* is amazingly faint in x-rays in comparison to central black holes observed in distant galaxies, even during its frequent x-ray flares. This suggests that this supermassive black hole has been starved by a lack of infalling material. In fact, the sharp Chandra image shows clouds of multi-million degree gas dozens of light-years across flanking (upper right and lower left) the central region -- evidence that violent events have cleared much material from the vicinity of the black hole.

Abell 1689 Warps Space

Two billion light-years away, galaxy cluster Abell 1689 is one of the most massive objects in the Universe. In this view from the Hubble Space Telescope's Advanced Camera for Surveys, Abell 1689 is seen to warp space as predicted by Einstein's theory of gravity -- bending light from individual galaxies which lie behind the cluster to produce multiple, curved images. The power of this enormous gravitational lens depends on its mass, but the visible matter, in the form of the cluster's yellowish galaxies, only accounts for about one percent of the mass needed to make the observed bluish arcing images of background galaxies. In fact, most of the gravitational mass required to warp space enough to explain this cosmic scale lensing is in the form of still mysterious dark matter. As the dominant source of the cluster's gravity, the dark matter's unseen presence is mapped out by the lensed arcs and distorted background galaxy images.

The Crab that Played with the Planet

Wandering through the constellation Taurus, Saturn made its closest approach to planet Earth last month, tilting its lovely rings toward appreciative skygazers while rising high in midnight skies. On January 4th and 5th, Saturn also crossed in front of the high and far-off Crab Nebula (M1), a cosmic cloud of debris from a stellar explosion and first on the list of astronomer Charles Messier's celestial sights. But Saturn and the Crab made poor playmates, as light from the bright planet overwhelmed the the diffuse nebula, all but hiding the Crab during the transit. Taken on January 2nd, a few days before their closest encounter, this composite digital image illustrates the problem. The subtle nebula is just visible at the right, while on the left, light from a drastically over-exposed Saturn overflows its pixels. Composited into the image is a correctly exposed picture of ringed Saturn with the Saturnian moons labeled. The well-exposed Saturn image was also taken on January 2nd, but captured with an exposure lasting only a fraction of a second, in contrast with the tens of seconds of exposure time required to reveal the Crab.

Apollo 17: Boulder in Stereo

Humans left the Moon over thirty years ago, but donning red-blue glasses (red for the left eye) you can share this excellent stereo perspective view of their last stomping ground. Recorded by Eugene Cernan, the scene depicts his fellow astronaut and geologist Harrison Schmitt next to a large split boulder on the floor of the narrow Taurus-Littrow valley located at the eastern edge of the lunar Mare Serenitatis. Parked nearby, their lunar rover is visible beyond the boulder at the right. During their stay the Apollo 17 astronauts explored the unusually dark terrain at the Taurus-Littrow landing site and deployed explosives to test the internal geology of the Moon. Apollo 17 returned the most lunar rocks and soil samples of any lunar mission.

A Spherule from Outer Space

When a meteorite strikes the Moon, the energy of the impact melts some of the splattering rock, a fraction of which might cool into tiny glass beads. Many of these glass beads were present in lunar soil samples returned to Earth by the Apollo missions. Pictured above is one such glass spherule that measures only a quarter of a millimeter across. This spherule is particularly interesting because it has been victim to an even smaller impact. A miniature crater is visible on the upper left, surrounded by a fragmented area caused by the shockwaves of the small impact. By dating many of these impacts, some astronomers estimate that cratering on our Moon increased roughly 500 million years ago and continues even today.

The Dumbbell Nebula in Hydrogen and Oxygen

The first hint of what will become of our Sun was discovered inadvertently in 1764. At that time, Charles Messier was compiling a list of "annoying" diffuse objects not to be confused with "interesting" comets. The 27th object on Messier's list, now known as M27 or the Dumbbell Nebula, is a planetary nebula, the type of nebula our Sun will produce when nuclear fusion stops in its core. M27 is one of the brightest planetary nebulae on the sky, and can be seen in the constellation Vulpecula with binoculars. It takes light about 1000 years to reach us from M27, shown above, digitally sharpened, in three isolated colors emitted by hydrogen and oxygen. Understanding the physics and significance of M27 was well beyond 18th century science. Even today, many things remain mysterious about bipolar planetary nebula like M27, including the physical mechanism that expels a low-mass star's gaseous outer-envelope, leaving an X-ray hot white dwarf.

0313-192: The Wrong Galaxy

Centered above is distant galaxy 0313-192, some one billion light-years away. Radio emission from the galaxy has been mapped by the National Radio Astronomy Observatory's Very Large Array and is shown in red, composited with a visible light image from the Hubble Space Telescope's new Advanced Camera for Surveys. Dust lanes and other features in the Hubble image as well as infrared Gemini telescope data demonstrate clearly that 0313-192 is a spiral galaxy seen edge-on. (Note the unrelated spiral galaxy seen face-on above and to the right.) For years, double cosmic clouds of radio emission such as those flanking this spiral galaxy's core have been studied and cataloged. But, at least until now, such radio sources were only known to arise from the cores of giant elliptical galaxies or in violent merging galaxy systems, making 0313-192 the wrong kind of galaxy to be found in this scenario. Astronomers are searching for clues to why this spiral galaxy, potentially similar to our own Milky Way, shows such powerful activity.

Ringed Planet Uranus

Yes it does look like Saturn, but Saturn is only one of four giant ringed planets in our Solar System. And while Saturn has the brightest rings, this system of rings and moons actually belongs to planet Uranus, imaged here in near-infrared light by the Antu telescope at the ESO Paranal Observatory in Chile. Since gas giant Uranus' methane-laced atmosphere absorbs sunlight at near-infrared wavelengths the planet appears substantially darkened, improving the contrast between the otherwise relatively bright planet and the normally faint rings. In fact, the narrow Uranian rings are all but impossible to see in visible light with earthbound telescopes and were discovered only in 1977 as careful astronomers noticed the then unknown rings blocking light from background stars. The rings are thought to be younger than 100 million years and may be formed of debris from the collision of a small moon with a passing comet or asteroid-like object. With moons named for characters in Shakespeare's plays, the distant ringed world Uranus was last visited in 1986 by the Voyager 2 spacecraft.

NGC 1700: Elliptical Galaxy and Rotating Disk

In spiral galaxies, majestic winding arms of young stars and interstellar gas and dust rotate in a disk around a bulging galactic nucleus. Elliptical galaxies seem to be simpler, randomly swarming with old stars and lacking gas and dust. So astronomers were excited to find that NGC 1700, a young elliptical galaxy about 160 million light-years away, shows evidence for a 90,000 light-year wide rotating disk of multi-million degree hot gas. The evidence comes from data recorded by the orbiting Chandra Observatory, whose sharp x-ray image of NGC 1700 is seen above. Balancing gravity, the rotation of the x-ray hot disk, the largest of its type yet discovered, gives the galaxy a pronounced boxy profile in this false-color picture. Theories about the origin of the disk suggest that NGC 1700 may be the result of a cosmic scale galactic merger, perhaps between a spiral and elliptical galaxy. NGC 1700 is just visible with small telescopes toward the flowing constellation Eridanus.

Stars and the Bubble Nebula

Seemingly adrift in a cosmic sea of stars and gas, this delicate, floating apparition is cataloged as NGC 7635 -- The Bubble Nebula. In this wide-angle view, the Bubble nebula lies at the center of a larger complex of shocked glowing gas about 11,000 light-years distant in the fair constellation Cassiopeia. NGC 7635 really is an interstellar bubble, blown by winds from the brightest star visible within the bubble's boundary. The bubble's expansion is constrained by the surrounding material. About 10 light-years in diameter, if the Bubble nebula were centered on the Sun, the Sun's nearest stellar neighbor, Alpha Centauri, would also be enclosed. This breathtaking picture is a combination of telescopic digital images made through broad color filters along with a narrow filter intended to transmit only the red light emitted by excited hydrogen atoms.

Filaments in the Cygnus Loop

Subtle and delicate in appearance, these are filaments of shocked interstellar gas -- part of the expanding blast wave from a violent stellar explosion. Recorded in November 1997 with the Wide Field and Planetary Camera 2 on board the Hubble Space Telescope, the picture is a closeup of a supernova remnant known as the Cygnus Loop. The nearly edge-on view shows a small portion of the immense shock front moving toward the top of the frame at about 170 kilometers per second while glowing in light emitted by atoms of excited hydrogen gas. Not just another pretty picture, this particular image has provided some dramatic scientific results. In 1999, researchers used it to substantially revise downward widely accepted estimates of distance and age for this classic supernova remnant. Now determined to lie only 1,440 light-years away, the Cygnus Loop is thought to have been expanding for 5 - 10 thousand years.

Fullerenes as Miniature Cosmic Time Capsules

Scientists have found, unexpectedly, tiny time capsules from billions of years in the past. The discovery involves small molecules that can apparently become trapped during the formation of large enclosed molecules known as fullerenes, or buckyballs. Luann Becker (UCSB) and collaborators recently found fullerenes in an ancient meteorite that fell to Earth about 30 years ago. Extra-terrestrial fullerenes inside the meteorite survived, and upon inspection, were not empty inside. The small molecules trapped inside are giving a glimpse of what the Solar System was like during its formation. Pictured above is a computer simulation showing a relatively small fullerene (60-atoms of carbon) situated above a hydrogenated silicon surface. How these fullerenes formed, how they survived, where else they can be found, and what else might be found inside these tiny time capsules is developing into an exciting area of research.

Io at Sunset

How tall are mountains on Jupiter's moon Io? One way to find out is to view them at sunset. Tall structures facing the Sun are then better-lit and cast long shadows. The above image highlights Mongibello Mons on the far left, a sharp ridge rising so high it would rank among the highest mountains on Earth. The violently changing surface of Io shows not only classic volcano cinder cones but also many thrust faults where the ground has fractured and created dramatic shear cliffs. The grayscale image was taken two years ago by the robot spacecraft Galileo currently orbiting Jupiter.

The Reflecting Dust Clouds of Orion

In the vast Orion Molecular Cloud complex, several bright blue nebulas are particularly apparent. Pictured above are two of the most prominent reflection nebulas - dust clouds lit by the reflecting light of bright embedded stars. The more famous nebula is M78, on the upper right, cataloged over 200 years ago. On the lower left is the lesser known NGC 2071. Astronomers continue to study these reflection nebulas to better understand how interior stars form. The Orion complex lies about 1500 light-years distant, contains the Orion and Horsehead nebulas, and covers much of the constellation of Orion.

M11: The Wild Duck Cluster

Many stars like our Sun were formed in open clusters. The above pictured open cluster, M11, contains thousands of stars and is just over five thousand light years distant. The stars in this cluster all formed together about 250 million years ago. The bright young stars in M11 appear blue. Open clusters, also called galactic clusters, contain fewer and younger stars than globular clusters. Also unlike globular clusters, open clusters are generally confined to the plane of our Galaxy. M11 is visible with binoculars towards the constellation of Scutum.

Launch of the Sun Pillar

On January 16, NASA's space shuttle Columbia roared into blue morning skies above Kennedy Space Center on STS-107, the first shuttle mission of 2003. But this is not a picture of that launch! It was taken on the morning of January 16 though, at sunrise, looking eastward toward Lake Ontario from just outside of Caledon, Ontario, Canada. In the picture a sun pillar, sunlight reflecting from ice crystals gently falling through the cold air, seems to shoot above the fiery Sun still low on the horizon. By chance, fog and clouds forming over the relatively warm lake look like billowing smoke from a rocket's exhaust plume and complete the launch illusion. Amateur photographer Lauri Kangas stopped on his way to work to record the eye-catching sun pillar launch.

Seyfert's Sextet

Known as Seyfert's Sextet, this intriguing group of galaxies lies in the head portion of the split constellation Serpens. The sextet actually contains only four interacting galaxies, though. Near the center of this Hubble Space Telescope picture, the small face-on spiral galaxy lies in the distant background and appears only by chance aligned with the main group. Also, the prominent condensation on the far right is likely not a separate galaxy at all, but a tidal tail of stars flung out by the galaxies' gravitational interactions. About 190 million light-years away, the interacting galaxies are tightly packed into a region around 100,000 light-years across, comparable to the size of our own Milky Way galaxy, making this one of the densest known galaxy groups. Bound by gravity, the close-knit group may coalesce into a single large galaxy over the next few billion years.

Palomar 13's Last Stand

Globular star cluster Palomar 13 has roamed the halo of our Milky Way Galaxy for the last 12 billion years. The apparently sparse cluster of stars just left of center in this composite color digital image, it is one of the smallest, faintest globular clusters known. (The bright foreground star near bottom is unrelated and creates the spiky imaging artifacts.) Observations spanning forty years indicate that Palomar 13's galactic halo orbit is a highly eccentric one which, every one or two billion years, brings it relatively close to the galactic center. With each close approach to the Milky Way's central regions, gravitational tidal forces strip away the delicately bound cluster stars. In fact, detailed present day studies offer evidence for a dramatic end to this dwindling cluster's tidal tug of war. Palomar 13's latest close approach was only about 70 million years ago. But, when Palomar 13 again approaches the galaxy, it could well turn out to be the cluster's last stand.

The Lyman Alpha Forest

We live in a forest. Strewn throughout the universe are "trees" of hydrogen gas that absorb light from distant objects. These gas clouds leave numerous absorption lines in a distant quasar's spectra, together called the Lyman-alpha forest. Distant quasars appear to be absorbed by many more Lyman-alpha clouds than nearby quasars, indicating a Lyman-alpha thicket early in our universe. The above image depicts one possible computer realization of how Lyman-alpha clouds were distributed at a redshift of 3. Each side of the box measures 30 million light-years across. Much remains unknown about the Lyman-alpha forest, including the real geometry and extent of the clouds, and why there are so many fewer clouds today.

BHR 71: Stars, Clouds, and Jets

What is happening to molecular cloud BHR 71? Quite possible, a binary star system is forming inside. Most stars in our Galaxy are part of binary star systems, but few have ever been seen in formation. Recent observations of dust-darkened Bok Globule BHR 71, however, show evidence for two young stars forming deep in the cloud, likely close enough to form a binary. Isolated BHR 71 spans about one light year and lies only about 600 light years away in the southern sky. The brighter embedded star -- not visible here -- is about 10 times as bright as the Sun and drives the jet that swept out the empty lane. The above four-color image was taken with a Very Large Telescope in Chile.

The Lost World of Lake Vida

A lake hidden beneath 19 meters of ice and gravel has been found near the bottom of the world that might contain an ecosystem completely separate from our own. In a modern version of Sir Arthur Conan Doyle's classic book Lost World, scientists are now plotting a mission to drill down into the lake and take out a small part to see what's there. Lake Vida, buried under Antarctic ice for over 2,500 years, is liquid only because of its high salt content. Previously, scientists drilled to within a few meters of the lake and indeed found frozen microbes. Their existence bolsters speculation that similar microorganisms could be found in frozen brine beneath the surface of Mars. If living organisms are found in Lake Vida, they may give an indication that life might even still exist under similar frozen ice-sheets, such as under the larger Lake Vostok, parts of Mars, and even moons of Jupiter such as Europa. Pictured above, a robot meteorological station continues to monitor surface conditions over the ice-sealed lake.

Orion's Horsehead Nebula

The Horsehead Nebula is one of the most famous nebulae on the sky. It is visible as the dark indentation to the red emission nebula seen above and to the right of center in the above photograph. The bright star on the left is located in the belt of the familiar constellation of Orion. The horse-head feature is dark because it is really an opaque dust cloud which lies in front of the bright red emission nebula. Like clouds in Earth's atmosphere, this cosmic cloud has assumed a recognizable shape by chance. After many thousands of years, the internal motions of the cloud will alter its appearance. The emission nebula's red color is caused by electrons recombining with protons to form hydrogen atoms. Also visible in the picture are blue reflection nebulae, which preferentially reflect the blue light from nearby stars.

Comet Kudo-Fujikawa: Days in the Sun

Cruising through the inner Solar System, new Comet Kudo-Fujikawa reached perihelion, its closest approach to the Sun, yesterday, January 29. Passing within 28.4 million kilometers of the Sun, this comet came much closer than innermost planet Mercury basking only 57.9 million kilometers from our parent star. So close to the Sun, comet Kudo-Fujikawa was extremely bright but impossible for earthbound observers to see against the solar glare. Still, the space-based SOHO observatory captured these views of the comet as it neared perihelion by using a coronograph's occulting disk to block the overwhelming sunlight. In the series of images, the size and location of the blocked-out Sun is indicated by white circles, while arrows point to the traveling comet's bright coma and developing tail. Though fading on its outbound journey, Kudo-Fujikawa should soon be visible to southern hemisphere comet-watchers in February's evening skies.

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