NASA Astronomy Picture of the Day 2001-10

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.

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 untethered 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.

The Planetary Nebula Show

What do the Owl, the Cat's Eye, the Ghost of Jupiter, and Saturn have in common? They're all planetary nebulae of course(!), glowing gaseous shrouds shed by dying sun-like stars as they run out of nuclear fuel. Beautiful to look at, the symmetric, planet-like shapes of these cosmic clouds, typically 1,000 times the size of our solar system, evoke their popular names. Flipping through digital pictures made by participants in the Kitt Peak National Observatory Visitor Center's Advanced Observing Program, astronomer Adam Block created this delightful animation. Ten different planetary nebula images are presented, each registered on the central star. In order, their catalog designations are NGC 1535, 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 phase in the life of a star lasts only about 10,000 years.

M74: The Perfect Spiral

If not perfect, then this spiral galaxy is at least one of the most photogenic. An island universe of about 100 billion stars, 30 million light-years away toward the constellation Pisces, NGC 628 or M74 presents a gorgeous face-on view to earthbound astronomers. Classified as an Sc galaxy, the grand design of M74's graceful spiral arms traced by bright blue star clusters and dark cosmic dust lanes, is similar in many respects to our own home galaxy, the Milky Way. Recorded with a 28 million pixel detector array, this impressive image celebrates first light for the Gemini Multi-Object Spectrograph (GMOS), a state-of-the-art instrument now operational at the 8-meter Gemini North telescope. The Gemini North Observatory gazes into the skies above Mauna Kea, Hawaii, USA, while its twin observatory, Gemini South, is scheduled to begin operations later this year from Cerro Pachón in central Chile.

A Flock of Stars

Only a few stars can be found within ten light-years of our lonely Sun, situated near an outer spiral arm of the Milky Way galaxy. But if the Sun were found within one of our galaxy's star clusters, thousands of stars might occupy a similar space. What would the night sky look like in such a densely packed stellar neighborhood? When Roger Hopkins took this picture at the Montezuma National Wildlife Refuge in the Finger Lakes region of western New York, USA, he was struck by this same notion. Appropriately, he had photographed a flock of starlings against the backdrop of a serene sunset. He then manipulated the image so that the black bird silhouettes were changed to white. The final picture dramatically suggests the tantalizing spectacle of approaching night in crowded skies above a cluster star world.

Hen 1357: New Born Nebula

This Hubble Space Telescope snapshot shows Hen-1357, the youngest known planetary nebula. Graceful, gentle curves and symmetry suggest its popular name - The Stingray Nebula. Observations in the 1970s detected no nebular material, but this image from March 1996 clearly shows the Stingray's emerging bubbles and rings of shocked and ionized gas. The gas is energized by the hot central star as it nears the end of its life, evolving toward a final white dwarf phase. The image also shows a companion star (at about 10 o'clock) within the nebula. Astronomers suspect that such companions account for the complex shapes and rings of this and many other planetary nebulae. This cosmic infant is about 130 times the size of our own solar system and growing. It is 18,000 light-years distant, in the southern constellation Ara.

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 street lamps 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.

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.

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 also because 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.

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 occasional 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.

VDB 142 in Cepheus

A gorgeous collection of dust and gas nebulae in the Northern Milky Way graces the high and far off constellation of Cepheus. With colors based on astronomical filters, this close up of the region highlights stars embedded in curiously shaped cosmic clouds. Near the central faint (9th magnitude) star in the image, dust clouds reflect the starlight, creating a bluish reflection nebula cataloged in 1966 as VDB 142. The area's bright reddish emission nebulae indicate the presence of clouds of atomic hydrogen gas. Stripped of electrons by invisible ultraviolet light, the hydrogen atoms emit their characteristic visible red light as electrons and atoms recombine. Sweptback clouds of obscuring dust, dark nebulae, are silhouetted against the bright background. Representing the stuff stars are made of, all these nebulae lie within the large young star cluster complex IC 1396, 3,000 light years from Earth.

Space Station and Space Shuttle: Backyard View

Knowing when and where to look, many enthusiastic sky gazers have been able to spot the International Space Station (ISS) as a bright star streaking through the twilight. But with a digital camera and a small telescope, recognizable images are possible too. Astronomer Ricardo Borba offers this example of the Space Shuttle Discovery docked with the ISS, recorded this August from his 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 atmospheric blurring caused most of the video frames to be indistinct, still the single best frame (left) from his video sequence is amazingly sharp. For comparison, he constructed a computer generated image (right) showing the approximate orientation of the Shuttle/ISS docking configuration based on virtual 3D models available on the web.

A Portrait of Saturn from Titan

This artistic portrait of Saturn depicts how it might look from Titan, Saturn's largest moon. In the foreground sits ESA's Huygens probe, which will be released by NASA's Cassini spacecraft and parachute to Titan's surface. Cassini will reach 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 lakes and an atmospheric chemistry like that found on early Earth. The Cassini spacecraft was launched in October 1997 and has now traveled beyond Jupiter.

Galileo Demonstrates the Telescope

Galileo Galilei made a good discovery great. Upon hearing at age 40 that a Dutch optician had invented a glass that made distant objects appear larger, 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. Galileo claimed that his observations only made sense if all the planets revolved around the Sun, as championed by Aristarchus and Copernicus, not the Earth, as was commonly believed then. The powerful Inquisition made Galileo publicly recant this conclusion, but today we know he was correct.

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.

A Newly Active Volcano on Jupiter's 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.

Mars Engulfed

For months now, Mars has been engulfed by a great dust storm, the biggest seen raging across the Red Planet in decades. As a result, these two Hubble Space Telescope storm watch images from late June and early September offer dramatically contrasting views of the martian surface. At left, the onset of smaller "seed" storms can be seen near the Hellas basin (lower right edge of Mars) and the 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 the warming of the upper martian atmosphere and cooling of the surface are still being monitored daily by instruments on board the Mars Global Surveyor spacecraft. The present condition of the martian atmosphere is also important to the aerobraking Mars Odyssey spacecraft, scheduled to arrive at the Red Planet next week.

Pluto: New Horizons

Pluto's horizon spans the foreground in this artist's vision, gazing sunward across that distant and not yet explored world. Titled New Horizons, the painting also depicts Pluto's companion, Charon, as a darkened, ghostly apparition with a luminous crescent against a starry background. Beyond Charon, the diminished Sun is immersed in a flattened cloud of zodiacal dust. Here, Pluto's ruddy colors are based on existing astronomical observations while imagined but scientifically tenable details provided by the artist include high atmospheric cirrus and dark plumes from surface vents, in analogy to Neptune's large moon Triton explored by the Voyager 2 spacecraft in 1989. Craters suggest bombardment by Kuiper Belt objects, a newly understood population of outer solar system bodies likely related to the Pluto-Charon system. NASA is now considering a future robotic reconnaissance mission to Pluto-Charon and the Kuiper Belt which could reach the distant worlds late in the next decade.

X-Ray Stars and Winds in the Rosette Nebula

This mosaic of x-ray images cuts a swath across the photogenic Rosette Nebula, a stellar nursery 5,000 light-years from Earth in the constellation Monoceros, the Unicorn. Constructed from data recorded by the orbiting Chandra X-ray Observatory, the mosaic spans less than 100 light-years and is color coded to show low energies in red and high energy x-rays in blue. At the upper right is the young star cluster NGC 2244, central to the Rosette Nebula itself. The hot outer layers of the massive stars are seen to be copious sources of x-rays, but a diffuse x-ray glow also pervades this cluster of newborn stars. Since these stars are so young (less than few million years old!) the diffuse x-ray emission is thought to be powered by energetic, colliding stellar winds rather than remnants of supernovae explosions, a final act in the life cycle of 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 to dense molecular gas, absorbing low energy x-rays while revealing the penetrating high energy x-rays from embedded stars.

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 your dial somewhere between US broadcast television channels 13 and 14. In the 1970s large dish antennas at three radio observatories, Jodrell Bank, MPIfR, and 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 spiraling along magnetic fields. In the resulting false color image, the galactic plane runs horizontally through the center, but no stars are visible. Instead, many of the bright sources near the plane are distant pulsars, star forming regions, and supernova remnants, while the grand looping structures are pieces of bubbles blown by local stellar activity. External galaxies like Centaurus A, located above the plane to the right of center, and the LMC (below and right) also shine in the Radio Sky.

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 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.

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 Matter Of Galaxy Clusters

Situated over 2,000,000,000 (two billion) light-years from Earth, galaxies in cluster Abell 2390 (top) and MS2137.3-2353 (bottom) are seen in the right hand panels above, false-color images from the Hubble Space Telescope. Corresponding panels on the left reveal each cluster's x-ray appearance 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 ... only multi-million degree hot intracluster gas which glows in high energy x-rays. But there lies a profound mystery. The total mass in the galaxies on the right, plus the mass of the hot gas on the left, falls far short of providing enough gravity to confine the hot gas within the galaxy clusters. In fact, the best accounting to date can only find 13 per cent (!) of the total matter necessary. Gravitational lens arcs visible in the deep Hubble images also indicate these clusters have much more mass than directly identifiable in the Chandra and Hubble data. Astronomers conclude that most of the cluster matter is dark matter, invisible even to the combined far-seeing eyes of these orbiting astrophysical observatories. What is the nature of this cosmic dark matter?

Odyssey at Mars

After an interplanetary journey lasting 200 days, the Mars Odyssey spacecraft has entered orbit around the Red Planet. This latest success is welcome as in the past, Mars has often seemed a difficult planet to visit. Beginning with the first Soviet attempts in 1960, around 30 missions have tried while only 10 or so have gone without serious mishap. Now that Mars Odyssey has arrived, its immediate future will involve aerobraking. Cautiously dipping into the martian atmosphere, the spacecraft will gradually adjust its present wide and elliptical 20-hour orbit to a circular 2-hour orbit only 400 kilometers above the planet's surface. Then, its instruments and cameras will focus on exploring the climate and geologic history of Mars, including the search for water and evidence of life-sustaining environments. In the artist's conception above, the spacecraft with wing-like solar panels is imagined firing its rocket engine for Mars orbit insertion over terrain seen in natural and false-color.

Elements in the Aftermath

Massive stars spend their brief lives furiously burning nuclear fuel. Through fusion at extreme temperatures and densities surrounding the stellar core, nuclei of light elements like Hydrogen and Helium are combined to heavier elements like Carbon, 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 debris enriched in heavier elements to be incorporated into other stars and planets (and people!). This detailed false-color x-ray image from the orbiting Chandra Observatory shows such a hot, expanding stellar debris cloud about 36 light-years across. Cataloged as G292.0+1.8, this young supernova remnant in the southern constellation Centaurus resulted from a massive star which exploded an estimated 1,600 years ago. Bluish colors highlight filaments of the mulitmillion degree gas which are exceptionally rich in Oxygen, Neon, and Magnesium. Just below and left of center, a point like object in the Chandra image suggests that the enriching supernova also produced a pulsar in its aftermath, a rotating neutron star remnant of the collapsed stellar core.

Sher 25: A Pending Supernova?

No supernova has ever been predicted. These dramatic stellar explosions that destroy stars and disperse elements that compose people and planets are not so well understood that astronomers can accurately predict when a star will explode - yet. Perhaps Sher 25 will be the first. Sher 25, designated by the arrow, is a blue supergiant star located just outside the star cluster and emission nebula 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 step that closely precedes a supernova. If so, Sher 25 may be within a few thousand years of its spectacular finale.

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.

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.

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.

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's modern 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.

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