NASA Astronomy Picture of the Day 2002-8

Sunspots and Solar Active Regions

July was a good month for sunspots ... really big sunspots. In fact, the full disk and inset pictures above show three large groups of spots, photographed only a few days ago on July 28. Together the sunspots span a region about thirty times the diameter of planet Earth. Now rotating behind the Sun's visible edge, these groups followed close on the heels of another enormous sunspot group which appeared in mid July. All of July's monster sunspot groups could be viewed without magnification, using safe solar observing methods of course. While individual sunspots are not numbered or cataloged, groups of sunspots, designated solar active regions, are given consecutive numbers as they appear on the visible solar disk. That numbering began on January 5, 1972 and on June 14, 2002, reached active region number 10,000. At the 10k mark no door prizes were given and no disasters plagued our fair solar system. But since June 14, active region reports often drop at least the leading digit, making these three active regions AR 0050, AR 0039, and AR 0044 (top left to bottom right).

Comet 57P Falls to Pieces

Comet 57P has fallen to pieces, at least 19 of them. Orbiting the Sun every 6 years or so this faint comet - also christened Comet 57P/du Toit-Neujmin-Delporte for its three 1941 co-discoverers - is simply 57th on the list of comets known to be periodic, beginning with Comet 1P/Halley. In mid July, responding to reports of a new object possibly associated with Comet 57P, astronomers were able to construct this mosaic of deep sky images identifying a surprising 19 fragments (circled) strung out behind the cometary coma and nucleus itself (far left). The full mosaic spans about a million kilometers at the distance of the comet, while the individual pieces detected are probably a few tens to a few hundred meters across. Stress produced as sunlight warmed the icy, rocky nucleus likely contributed to the fragmentation. In fact, when last seen passing through the inner solar system in 1996, Comet 57P brightened unexpectedly, indicating a sudden increase in surface activity.

The Galactic Center - A Radio Mystery

Tuning in to the center of our Milky Way galaxy, radio astronomers explore a complex, mysterious place. A premier high resolution view, this startlingly beautiful picture covers a 4x4 degree region around the galactic center. It was constructed from 1 meter wavelength radio data obtained by telescopes of the Very Large Array near Socorro, New Mexico, USA. The galactic center itself is at the edge of the extremely bright object labeled Sagittarius (Sgr) A, suspected of harboring a million solar mass black hole. Along the galactic plane which runs diagonally through the image are tortured clouds of gas energized by hot stars and bubble-shaped supernova remnants (SNRs) - hallmarks of a violent and energetic cosmic environment. But perhaps most intriguing are the arcs, threads, and filaments which abound in the scene. Their uncertain origins challenge present theories of the dynamics of the galactic center.

Spiral Galaxy NGC 2997 from VLT

NGC 2997 is a grand design spiral galaxy. Its small nucleus and sprawling spiral arms give it a type Sc designation. NGC 2997, pictured above, is speeding away from us at about 1100 kilometers per second, which would place it at about 55 million light years distant, given current estimates of the expansion rate of our universe. NGC 2997 is thought to have a mass of about 100 billion times that of our Sun, but is probably less massive than our own Milky Way galaxy. NGC 2997 is not seen face-on - it is thought tilted by about 45 degrees. NGC 2997 is particularly notable for a nucleus surrounded by a chain of hot giant clouds of ionized hydrogen.

Rays from an Unexpected Aurora

This aurora was a bit of a surprise. For starters, last Friday morning, no intense auroral activity was expected at all. Possibly more surprising, however, the aurora appeared to show an usual structure of green rays from some locations. In the above image, captured from North Dakota, USA, a picket fence of green rays stretches toward the horizon. Mirroring the green rays is a red band, somewhat rare in its own right. Lights from the cities of Bismarck and Mandan are visible near the horizon. Large sunspot groups indicate that activity from the currently active Sun is relatively likely, possibly causing other streams of energetic particles to cascade onto the Earth and so causing more auroras.

Muon Wobble Possible Door to Supersymmetric Universe

How fast do fundamental particles wobble? A surprising answer to this seemingly inconsequential question is coming out of Brookhaven National Laboratory in New York, USA and may not only indicate that the Standard Model of Particle Physics is incomplete but also that our universe is filled with a previously undetected type of fundamental particle. Specifically, the muon, a particle with similarities to a heavy electron, has had its relatively large wobble under scrutiny since 1999 in an experiment known as g-2 (gee-minus-two), pictured above. The result galvanizes other experimental groups around the world to confirm it, and pressures theorists to better understand it. The rate of wobble is sensitive to a strange sea of virtual particles that pop into and out of existence everywhere. The unexpected wobble rate may indicate that this sea houses virtual particles that include nearly invisible supersymmetric counterparts to known particles. If so, a nearly invisible universe of real supersymmetric particles might exist all around us.

Gomez's Hamburger: A Proto-Planetary Nebula

What, in heaven, is that? Sometimes astronomers see things on the sky they don't immediately understand. In 1985 this happened to Arturo Gomez, and the object became known as Gomez's Hamburger for its distinctive yet familiar shape. After some investigation, the object was identified as a proto-planetary nebula, a gas cloud emitted by a Sun-like star just after its central hydrogen fuel has all been fused to helium. Gomez's Hamburger is on its way to becoming a full-fledged planetary nebula in a few thousand years. The light seen (the bun) is reflected by dust from the central star, although the star itself is obscured by a thick dust disk that runs across the middle (the patty). Gomez's Hamburger, pictured above in a recent image from the Hubble Space Telescope, is only a fraction of a light year across but located approximately 10,000 light years away towards the constellation of Sagittarius.

Ancient Volcanos of Mars

Findings of ancient martian microbial fossils in meteorites and liquid water related features on Mars' surface are currently controversial issues. But one thing long established by space-based observations of the Red Planet is the presence of volcanos, as Mars supports some of the largest volcanos in the solar system. This synthetic color picture recorded in March by the Mars Global Surveyor spacecraft shows two of them, Ceraunius Tholus (leftmost) and Uranius Tholus. Found north of the Tharsis region of truly large martian volcanos, these are actually two relatively small volcanos, Ceraunius Tholus being only about the size of the Big Island of Hawaii on planet Earth. Impact craters which overlay the volcanic martian terrain indicate that these volcanos are themselves ancient and inactive. North is to the right and the scene is illuminated by sunlight from the top left. A light region of dust deposited by recent global dust storms lies on the lower left flank of Ceraunius Tholus, whose summit crater is about 25 kilometers across.

Fireworks and Shooting Stars

erimenting with a new telescope and camera, photographer Jim Steele captured this surreal but festive image of fireworks in the night sky above Ashland, Oregon. The date was July 4th and the fiery streaks were part of the traditional annual celebration of independence day in the United States. Fiery streaks from another annual event will revisit dark skies this weekend, as shooting stars arc through the night during the much anticipated Perseid Meteor Shower. Perseid meteors are actually bits of dust from the periodic Comet Swift-Tuttle and once each year planet Earth orbits through Swift-Tuttle's cometary dust stream. As the comet dust enters Earth's atmosphere traveling at tens of kilometers per second, the particles are vaporized leaving bright and sometimes colorful trails. While Perseid meteors can be viewed over the next few nights, this year's shower is expected to peak on August 12 and 13 with a rate of dozens or more meteors per hour visible in moonless early morning skies.

Earth at Night

This is what the Earth looks like at night. Can you find your favorite country or city? Surprisingly, city lights make this task quite possible. Human-made lights highlight particularly developed or populated areas of the Earth's surface, including the seaboards of Europe, the eastern United States, and Japan. Many large cities are located near rivers or oceans so that they can exchange goods cheaply by boat. Particularly dark areas include the central parts of South America, Africa, Asia, and Australia. The above image is actually a composite of hundreds of pictures made by the orbiting DMSP satellites. (Editor's note: This image has become an email-attachment phenomenon! It has also generated many print requests. Unfortunately, we do not sell prints. However, a high-resolution digital version of the image is available (click here or here).

A Perseid Meteor

The ongoing Perseid Meteor Shower should be at its strongest on August 12 and 13. The best time to watch will be between 2:00 AM and dawn on Monday morning (so plan on setting your alarm tonight!) and then again on Tuesday. In dark, moonless, predawn skies you may see dozens of meteors per hour. Grains of cosmic sand and gravel shed from Comet Swift-Tuttle will streak across the sky as they vaporize during entry into Earth's atmosphere. Tracing the meteor trails backwards, experienced skygazers will find they converge on the constellation Perseus, thus this annual meteor shower's name. Pictured above is a Perseid meteor from 1993. The colors are representative but digitally enhanced. As the meteor streaked across the night sky, different excited atoms emitted different colors of light. The origin of the green tinge visible at the right is currently unknown, however, and might result from oxygen in Earth's atmosphere.

The Colors and Mysteries of Centaurus A

Why is spiral galaxy Centaurus A in so much turmoil? The above composite image shows different clues to the unusual galaxy's past in different bands of light. In low energy radio waves, shown in red, lobes across the thick swath of dust glow brightly. In more energetic radio waves, depicted in green, a bright jet is seen emanating from the galaxy's center. In optical light, shown in white, the stars that compose much of the galaxy are visible. Recently, Centaurus A has recently been imaged in X-ray light by the Chandra X-ray Observatory. The X-rays, depicted in blue, show arcs of hot gas shooting out from the center in an explosion that likely happened about 10 million years ago. One hypothesis that would explain the turmoil would be if Centaurus A devoured a smaller galaxy about 100 million years ago.

Contemplating the Sky

Have you contemplated your sky recently? Last night was a good one for midnight meditators at many northerly locations as meteors from the Perseid meteor shower frequently streaked through. The Perseid meteor shower has slowly been building to a crescendo but should continue to be rewarding tonight and into the week. Pictured above on August 1, a group of celestial sightseers near Quebec, Canada are treated to a dark and wondrous night sky that contained bright stars, green auroras, the band of our Milky Way galaxy, a majestic Moon rising, the International Space Station slowly gliding by, and the occasional flash of a Perseid meteor. Although no meteors were caught in this frame, the Big Dipper remained quite prominent.

Giant Emission Nebula NGC 3603 in Infrared

NGC 3603 is the largest region of glowing gas in our Milky Way galaxy. Spanning over 20 light years across, the giant emission nebula (HII region) is home to a massive star cluster, thick dust pillars, and a star about to explode. NGC 3603 was captured above in infrared light by a Two Micron All Sky Survey (2MASS) telescope. The young star cluster near the center heats the region's mostly hydrogen gas. Many stars in the cluster are estimated to be about one million years old, much less than the five billion-year age of our Sun. NGC 3603 lies approximately 20,000 light years away toward the constellation of Carina.

Meteors and Northern Lights

Skygazers report that the annual Perseid meteor shower went pretty much as predicted, producing a meteor every few minutes during the dark early morning hours of August 12 and 13. And as the constellation Perseus rose above the horizon on the night of August 11, astrophotographer Wade Clark was anticipating recording images of the flashing meteor trails from the Mt. Baker Ski Area in northwest Washington, USA. But Clark was also treated to a colorful display of northern lights. As a result, the stars of Perseus are arrayed near the center of his well composed skyscape along with trails of Perseid meteors all viewed through the auroral glow. The alluring scene might look familiar to watchers of bygone Perseids. For many, views of the meteor shower in 2000 also coincided with auroral displays, courtesy of the active Sun.

Rainbow Perseid

While meteors do show colors, the colors aren't always seen with the unaided eye. Still, high speed color film recorded this rainbow-like trail as a meteor streaked through the early morning sky on August 13 above Sedona, Arizona, USA. Part of the annual Perseid meteor shower, this bit of dust from the tail of Comet Swift-Tuttle entered Earth's atmosphere at over 200,000 kilometers per hour. The trail it left glowed briefly as friction with the atmosphere vaporized the dust grain and ionized atoms along its path. The initial green color is thought to be the glow from oxygen in the atmosphere at altitudes above 100 kilometers or so, while sodium atoms and other constituents of the cometary dust grain itself contribute to the orange hues.

Asteroid 2002 NY40

Asteroid 2002 NY40 will fly by planet Earth early in the morning August 18 Universal Time (late in the evening August 17 Eastern Daylight Time). Approaching to within about 530,000 kilometers or 1.3 times the Earth-Moon distance 2002 NY40 will definitely not be close enough to pose any danger of collision. But it will be close enough and just bright enough for experienced skygazers to see this 800 meter wide space rock in a small telescope or binoculars as it glides quickly through northern skies past the bright star Vega. It will also be close enough to ping with radar, and asteroid hunters using the large Arecibo radio telescope in Puerto Rico expect to determine the three dimensional outline of 2002 NY40. Similar investigations of other near Earth asteroids have revealed some surprising shapes. In this five minute time exposure, recorded at Cerro Tololo Inter-American Observatory on August 14, 2002 NY40 shows itself as a long smudge as it moves against a background of faint stars in the constellation Aquarius.

Earth's North Magnetic Pole

A magnetic compass does not point toward the true North Pole of the Earth. Rather, it more closely points toward the North Magnetic Pole of the Earth. The North Magnetic Pole is currently located in northern Canada. It wanders in an elliptical path each day, and moves, on the average, more than forty meters northward each day. Evidence indicates that the North Magnetic Pole has wandered over much of the Earth's surface in the 4.5 billion years since the Earth formed. The Earth's magnetic field is created by Earth's partially ionized outer core, which rotates more rapidly than the Earth's surface. Indicated in the above picture is Ellef Ringnes Island, the location of Earth's North Magnetic Pole in 1999.

Roque de los Muchachos Observatory

Above the clouds, atop an island off the coast of Africa, a group of cutting-edge telescopes inspects the universe. Pictured above are telescopes at Roque de los Muchachos Observatory on La Palma, one of the Canary Islands, Spain. The site is one of the premier observing locations on Earth. The telescopes pictured are, from left to right, the Carlsberg Meridian Telescope, the 4.2-meter William Herschel Telescope, the Dutch Open Telescope, the Swedish Solar Tower, the 2.5-meter Isaac Newton Telescope, and the 1.0-meter Jacobus Kapteyn Telescope. Pioneering observations made recently by these telescopes include stars and galaxies forming early in our universe, comets breaking up, and evidence for planets around Sun-like stars.

The Universe in Hot Gas

Where is most of the normal matter in the Universe? Recent observations from the Chandra X-ray Observatory confirm that it is in hot gas filaments strewn throughout the universe. "Normal matter" refers to known elements and familiar fundamental particles. Previously, the amount of normal matter predicted by the physics of the early universe exceeded the normal matter in galaxies and clusters of galaxies, and so was observationally unaccounted for. The Chandra observations found evidence for the massive and hot intergalactic medium filaments by noting a slight dimming in distant quasar X-rays likely caused by hot gas absorption. The above image derives from a computer simulation showing an expected typical distribution of hot gas in a huge slice of the universe 2.7 billion light-years across and 0.3 billion light years thick. The distribution of much more abundant dark matter likely mimics the normal matter, although the composition of the dark matter remains mysterious. Both the distribution and the nature of the even more abundant dark energy also remain unknown.

Spiral Galaxy NGC 300

NGC 300 is so interesting because it is so normal. An Sc-type spiral galaxy in the nearby Sculptor group of galaxies, NGC 300 shows typical flowing blue spiral arms, an expected compact nucleus, and the requisite amount of stars, star clusters, and nebulae. Therefore, studying NGC 300 should indicate how, exactly, a normal spiral galaxy works. Toward this goal, NGC 300 and the surrounding area were studied in exquisite detail, creating and combining a series of high-resolution images to create the above conglomerate picture. NGC 300 lies only 7 million light years away, spans nearly the same amount of sky as the full moon, and is visible with a small telescope toward the constellation of Sculptor.

Shell Game in NGC 300

Featured in color in yesterday's episode, big, beautiful, face-on spiral galaxy NGC 300 is seen here through a narrow filter that transmits only the red light of hydrogen atoms. Ionized by energetic starlight, a hydrogen atom emits the characteristic red H-alpha light as its single electron is recaptured and transitions to lower energy states. As a result, this image of NGC 300 is dominated by regions filled with massive, young stars and shell-shaped clouds of hydrogen gas hundreds to thousands of light-years across. Formed in groups called OB associations, the stars are likely only a few million years young. The hydrogen clouds are glowing nebulae or HII regions that have been sculpted by the strong stellar winds and ultraviolet radiation. While picking out your favorite cosmic shell in this picture, don't be misled by the relatively bright foreground stars located in our own Milky Way galaxy. They often show spikes and rings caused by the telescope and camera system.

Island Universe, Cosmic Sand

On August 13, while counting Perseid meteors under dark, early morning Arizona skies, Rick Scott set out to photograph their fleeting but fiery trails. The equipment he used included a telephoto lens and fast color film. After 21 pictures he'd caught only two meteors, but luckily this was one of them. Tracking the sky, his ten minute long exposure shows a field of many stars in our own Milky Way galaxy, most too faint to be seen by the unaided eye. Flashing from lower left to upper right, the bright meteor would have been an easy eyeful though, as friction with Earth's atmosphere vaporized the hurtling grain of cosmic sand, a piece of dust from Comet Swift-Tuttle. Just above and left of center, well beyond the stars of the Milky Way, lies the island universe known as M31 or the Andromeda galaxy. The visible meteor trail begins about 100 kilometers above Earth's surface, one of the closest celestial objects seen in the sky. In contrast, Andromeda, about 2 million light-years away, is the most distant object easily visible to the naked-eye.

Cas A Supernova Remnant in X-Rays

The complex shell of a star seen to explode 300 years ago is helping astronomers to understand how that star exploded. This Chandra Observatory image of supernova remnant Cassiopeia A (Cas A) shows unprecedented detail in three x-ray colors. The relationship between brightness, color, and position of material in the image indicates where in the star this material was just before the explosion. Bright knots on the left, for example, contain little iron, and so are hypothesized to originate from a higher layer than outer red filaments, which are iron rich. The blue region on the right is seen through absorbing dust, and so appears depleted of low-energy x-rays. It takes light ten years to cross the gas shell of the Cas A supernova remnant, which is 10,000 light-years distant. Most of the elements that make people and planets were produced in supernova explosions.

Nebula Nova Cygni Turns On

Old photographs show no evidence of the above nebula. In 1992, a white dwarf star toward the constellation of Cygnus blew off its outer layers in a classical nova explosion: an event called Nova Cygni 1992. Light flooded the local interstellar neighborhood, illuminated this existing gas cloud, excited the existing hydrogen, and hence caused the red emission. The only gas actually expelled by the nova can be seen as a small red ball just above the photograph's center. Eventually, light from the nova shell will fade, and this nebula will again become invisible!

The Mysterious Voynich Manuscript

The ancient text has no known title, no known author, and is written in no known language: what does it say and why does it have many astronomy illustrations? The mysterious book was once bought by an emperor, forgotten on a library shelf, sold for thousands of dollars, and later donated to Yale. Possibly written in the 15th century, the over 200-page volume is known most recently as the Voynich Manuscript, after its (re-)discoverer in 1912. Pictured above is an illustration from the book that appears to be somehow related to the Sun. The book labels some patches of the sky with unfamiliar constellations. The inability of modern historians of astronomy to understand the origins of these constellations is perhaps dwarfed by the inability of modern code-breakers to understand the book's text. The book remains in Yale's rare book collection under catalog number "MS 408."

Valles Marineris: The Grand Canyon of Mars

The largest canyon in the Solar System cuts a wide swath across the face of Mars. Named Valles Marineris, the grand valley extends over 3,000 kilometers long, spans as much as 600 kilometers across, and delves as much as 8 kilometers deep. By comparison, the Earth's Grand Canyon in Arizona, USA is 800 kilometers long, 30 kilometers across, and 1.8 kilometers deep. The origin of the Valles Marineris remains unknown, although a leading hypothesis holds that it started as a crack billions of years ago as the planet cooled. Recently, several geologic processes have been identified in the canyon. The above mosaic was created from over 100 images of Mars taken by Viking Orbiters in the 1970s.

3D Mars: Northern Terra Meridiani

In this spectacular 3D stereoscopic view from orbit, steep-sided, flat-topped hills stand above the Terra Meridiani region of Mars. Seen best with red/blue glasses (red for the left eye), the structures are reminiscent of buttes and mesas found in southwestern areas of the North American continent on planet Earth. Like their terrestrial counterparts, these layered martian outcrops apparently formed of hard sedimentary rocks with surrounding softer material eroded away. The possibility that surface water laid down the formations makes the Terra Meridiani region a tempting target for future exploration by Mars landers. But alternative explanations include material deposited by wind or accumulations of volcanic ash. The area pictured is about 3 kilometers across, maybe a thirty minute walk over flat ground. Terrestrial rock climbers take note; you and your equipment would only weigh around 1/3 as much in the lower martian surface gravity.

The Pelican in the Swan

The Pelican Nebula, also known as IC 5070, lies about 2,000 light-years away in the high and far-off constellation of Cygnus, the Swan. This picture spans a portion of the magnificent nebula about 30 light-years wide. Fittingly, this cosmic pelican is found just off the east "coast" of the North America Nebula, another surprisingly familiar looking emission nebula in Cygnus. In fact, the Pelican and North America nebulae are part of the same large star forming region. The two glowing nebulae appear separated from our vantage point by a large obscuring dust cloud running across the upper left corner in this gorgeous color view. Within the Pelican Nebula, dark dust clouds also help define the eye and long bill, while a bright front of ionized gas suggests the curved shape of the head and neck. Even though it is almost as close as the Orion Nebula, the stellar nursery marked by the Pelican and North America nebulae has proven complex and difficult to study.

Semeis 147: Supernova Remnant

It's easy to get lost following the intricate filaments in this stunningly detailed image of faint supernova remnant Simeis 147. Seen towards the constellation Taurus it covers nearly 3 degrees (6 full moons) on the sky corresponding to a width of 150 light-years at the stellar debris cloud's estimated distance of 3,000 light-years. On three separate nights in December 2001 and January 2002 astronomer Steve Mandel accumulated a total of over eight hours of exposure time to compose this image. He used an astronomical CCD camera, telephoto lens, and his specially designed adapter to allow such wide-field digital imaging. He also used a narrow H-alpha filter to transmit only the the light from recombining hydrogen atoms in the expanding nebulosity, defining the regions of shocked, glowing gas. This supernova remnant has an apparent age of about 100,000 years (light from the original explosion first reached Earth 100,000 years ago) but it is not the only aftermath of the massive stellar explosion. The cosmic catastrophe also left behind a spinning neutron star or pulsar, all that remains of the star's dense core.

history record