http://www.acme.com/jef/apod/ The Astronomy Picture of the Day is a wonderful web site that puts up a different astronomy-related picture every day. However, the site does not have an RSS feed. This page fixes that deficiency. ]]> en-us Fri, 03 Jul 2009 13:06:00 GMT ACME Labs custom shell script jef@mail.acme.com webmaster@mail.acme.com http://www.acme.com/jef/apod/apod.GIF http://www.acme.com/jef/apod/ http://antwrp.gsfc.nasa.gov/apod/ap090703.html Fri, 03 Jul 2009 13:06:00 GMT This year Aphelion, the point in Earth's elliptical orbit when it is farthest from the Sun, occurs tomorrow, July 4th. Of course, that doesn't affect the seasons on our fair planet. Those are determined by the tilt of Earth's axis of rotation and not Earth's distance from the Sun, so July is still winter in the south and summer in northern hemisphere. But it does mean that on July 4th the Sun will be at its smallest apparent size. This composite neatly compares two pictures of the Sun taken with the same telescope and camera on the dates of Perihelion (closest approach) and Aphelion in 2008. The image labels include Earth's distance in kilometers from the Sun on the two dates. Otherwise difficult to notice, the change in the Sun's apparent diameter between Perihelion and Aphelion is clear. The difference amounts to a little over 3 percent. ]]> http://antwrp.gsfc.nasa.gov/apod/ap090702.html Thu, 02 Jul 2009 13:06:00 GMT Dubbed a Lyman-alpha blob, an enormous cloud of hydrogen gas spans several hundred thousand light-years in this remarkable image (left), a composite of x-ray, optical, and infrared data from space and ground based observatories. The gigantic, amoeba-like structure is seen as it was when the universe was a mere 2 billion years old (about 12 billion years ago). Lyman-alpha blobs are so called because they strongly emit radiation due to the Lyman-alpha emission line of hydrogen gas. Normally, Lyman-alpha emission is in the ultraviolet part of the spectrum, but Lyman-apha blobs are so distant, their light is redshifted to (longer) optical wavelengths. X-ray data (blue) indicates the presence of a supermassive black hole feeding at the center of an active galaxy embedded in the blob. Illustrated close up in the right hand panel, radiation and outflows from the active galaxy are thought to be a source for energizing and heating the blob's hydrogen gas. In fact, Lyman-alpha blobs could represent an early phase in galaxy formation where the heating is so great it begins to limit further rapid growth of active galaxies and their supermassive black holes. ]]> http://antwrp.gsfc.nasa.gov/apod/ap090701.html Wed, 01 Jul 2009 13:06:01 GMT This intriguing trio of galaxies is sometimes called the Draco Group, located in the northern constellation of (you guessed it) Draco. From left to right are edge-on spiral NGC 5981, elliptical galaxy NGC 5982, and face-on spiral NGC 5985 -- all within this single telescopic field of view spanning a little more than half the width of the full moon. While the group is far too small to be a galaxy cluster and has not been cataloged compact group, these galaxies all do lie roughly 100 million light-years from planet Earth. On close examination with spectrographs, the bright core of the striking face-on spiral NGC 5985 shows prominent emission in specific wavelengths of light, prompting astronomers to classify it as a Seyfert, a type of active galaxy. Not as well known as other tight groupings of galaxies, the contrast in visual appearance makes this triplet an attractive subject for astrophotographers. This impressively deep exposure of the region also reveals faint and even more distant background galaxies. ]]> http://antwrp.gsfc.nasa.gov/apod/ap090630.html Tue, 30 Jun 2009 13:06:02 GMT Here are some familiar shapes in unfamiliar locations. This emission nebula on the left is famous partly because it resembles Earth's continent of North America. To the right of the North America Nebula, cataloged as NGC 7000, is a less luminous nebula that resembles a pelican dubbed the Pelican Nebula. The two emission nebula measure about 50 light-years across, are located about 1,500 light-years away, and are separated by a dark absorption cloud. This spectacular image captures the nebulas, bright ionization fronts, and fine details of the dark dust. The nebulae can be seen with binoculars from a dark location. Look for a small nebular patch north-east of bright star Deneb in the constellation of Cygnus. It is still unknown which star or stars ionize the red-glowing hydrogen gas. ]]> http://antwrp.gsfc.nasa.gov/apod/ap090629.html Mon, 29 Jun 2009 13:06:01 GMT Japan's Kaguya spacecraft crashed into the Moon last week, as planned. Officially named the Selenological and Engineering Explorer (SELENE), the spacecraft was given the nickname Kaguya after the princess in the Japanese folklore story The Tale of the Bamboo Cutter. Pictured above is a movie taken by Kaguya during the last orbit of its twenty-month lunar mission. A desolate, hilly, and cratered terrain passes underneath as the spacecraft barely clears a few peaks. At the movie's end, the spacecraft disappears into darkness near GILL crater. Robotic SELENE carried thirteen scientific instruments and two HDTV cameras. The groundbreaking mission took data on lunar topology and composition that are being used to better understand the origin and history of Earth's unique and ancient companion. Data and images from Kayuga and the recently launched Lunar Reconnaissance Orbiter could be used to choose good locations to land future Moon-exploring astronauts. ]]> http://antwrp.gsfc.nasa.gov/apod/ap090628.html Sun, 28 Jun 2009 13:06:03 GMT Do underground oceans vent through the tiger stripes on Saturn's moon Enceladus? Long features dubbed tiger stripes are known to be spewing ice from the moon's icy interior into space, creating a cloud of fine ice particles over the moon's South Pole and creating Saturn's mysterious E-ring. Evidence for this has come from the robot Cassini spacecraft now orbiting Saturn. Pictured above, a high resolution image of Enceladus is shown from a close flyby. The unusual surface features dubbed tiger stripes are visible on in false-color blue. Why Enceladus is active remains a mystery, as the neighboring moon Mimas, approximately the same size, appears quite dead. Most recently, an analysis of dust captured by Cassini found evidence for sodium as expected in a deep salty ocean. Conversely however, recent Earth-based observations of ice ejected by Enceladus into Saturn's E-Ring showed no evidence of the expected sodium. Such research is particularly interesting since such an ocean would be a candidate to contain life. ]]> http://antwrp.gsfc.nasa.gov/apod/ap090627.html Sat, 27 Jun 2009 13:06:01 GMT This panoramic image of a starry night looks across a dry, desolate landscape. The magnificent view was recorded from Tassili National Park, in the heart of the Sahara desert in southern Algeria. Rising above eroded sandstone cliffs, the celestial menagerie of constellations includes Draco the Dragon, Cygnus the Swan, Aquila the Eagle, and Scorpius the Scorpion. Ruling planet Jupiter shines through clouds very close to the horizon near picture center, while star clouds of the Milky Way arc through Sagittarius above the rocks at the far right. Bright blue stars Deneb, in Cygnus, and Altair, in Aquila, also shine in the starry night along with Scorpius' bright yellowish star Antares, the rival of Mars. Prehistoric skygazers surely witnessed a similar sky. In addition to dramatic sandstone formations, the Tassili region is noted for rock art and archaeological sites dating to Neolithic times when the local climate was wetter. ]]> http://antwrp.gsfc.nasa.gov/apod/ap090626.html Fri, 26 Jun 2009 13:06:01 GMT This six month long exposure compresses the time from solstice to solstice (~ December 21, 2008 to June 20, 2009) into a single point of view. Dubbed a solargraph, the unconventional picture was recorded with a pinhole camera made from an aluminum can lined with a piece of photographic paper. Fixed to a single spot for the entire exposure, the simple camera continuously records the Sun's daily path as a glowing trail burned into the photosensitive paper. Breaks and gaps in the trails are caused by cloud cover. In this case, the spot was chosen to look out from inside a radio telescope at the Ondrejov Observatory in the Czech Republic. At the end of the exposure, the paper was removed from the can and immediately scanned digitally. Contrasts and colors were then enhanced and added to the digital image. Of course, in December, the Sun trails begin lower down at the northern hemisphere's winter solstice. The trails climb higher in the sky as the June 21st summer solstice approaches. ]]> http://antwrp.gsfc.nasa.gov/apod/ap090625.html Thu, 25 Jun 2009 13:06:01 GMT From 400 kilometers above planet Earth, the Expedition 20 Crew onboard the International Space Station (ISS) was able to witness a remarkable event from a remarkable vantage point -- the June 12 eruption of the Sarychev Peak Volcano. The active volcano is located in Russia's Kuril Island chain, stretching to the northeast of Japan. Emphasizing the orbital perspective, this stunning color stereo view was made by combining two images from the ISS and is intended to be viewed with red/blue glasses (red for the left eye). Punching upwards into the atmosphere at an early stage of the eruption, the volcanic plume features a brown column of ash topped with a smooth, bubble-like, white cloud that is likely water condensation. Below, a cloud of denser grey ash slides down the volcanic slope. About 1.5 kilometers of the island coastline is visible at ground level. The evolving ash plume posed no danger to the Expedition 20 crew, but commercial airline flights were diverted away from the region to minimize the danger of engine failures from ash intake. ]]> http://antwrp.gsfc.nasa.gov/apod/ap090624.html Wed, 24 Jun 2009 13:06:01 GMT Sometimes it's night on the ground but day in the air. As the Earth rotates to eclipse the Sun, sunset rises up from the ground. Therefore, at sunset on the ground, sunlight still shines on clouds above. Under usual circumstances, a pretty sunset might be visible, but unusual noctilucent clouds float so high up they can be seen well after dark. Pictured above last week, a network of noctilucent clouds cast an eerie white glow after dusk, beyond a local field near Potsdam, Germany. Although noctilucent clouds are thought to be composed of small ice-coated particles, much remains unknown about them. Satellites launched to help study these clouds includes Sweden's Odin and NASA's AIM. Recent evidence indicates that at least some noctilucent clouds result from freezing water exhaust from Space Shuttles. ]]> http://antwrp.gsfc.nasa.gov/apod/ap090623.html Tue, 23 Jun 2009 13:06:02 GMT 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. In fact, Barnard 68 itself has recently been found likely to collapse and form a new star system. It is possible to look right through the cloud in infrared light. ]]> http://antwrp.gsfc.nasa.gov/apod/ap090622.html Mon, 22 Jun 2009 13:06:01 GMT This rocket is headed for the Moon. Pictured above, a huge Altas V rocket roared off the launch pad last week to start NASA's first missions to Earth's Moon in 10 years. The rocket is carrying two robotic spacecraft. The Lunar Reconnaissance Orbiter (LRO) is scheduled to orbit and better map the Moon, search for buried and hidden ice, and return many high resolution images. Some images will be below one-meter in resolution and include images of historic Apollo landing sites. Exploratory data and images should allow a more informed choice of possible future astronaut landing sites. The Lunar CRater Observation and Sensing Satellite (LCROSS) is scheduled to monitor the controlled impact of the rocket's upper stage into a permanently shadowed crater near the Moon's south pole. This impact, which should occur in about three months, might be visible on Earth through small telescopes. ]]> http://antwrp.gsfc.nasa.gov/apod/ap090621.html Sun, 21 Jun 2009 13:06:02 GMT Today, the sun will stay in the sky longer than any other day of the year, as seen from the northern hemisphere of Earth. Named the Summer Solstice, today's maximum daylight is indicative of the high amount of sunlight this time of year that is primarily responsible for the heat of the summer season. At the north pole and for all places above the arctic circle, there will be no night -- the entire day today will be lit by sunlight. The situation is reversed in Earth's southern hemisphere, where today has the least sunlight of any day. Today's solstice is commemorated above by a well-planned picture of our five billion year old Sun rising behind the 2,500 year old Parthenon in Greece. Trees and birds occupy the foreground, while a modern crane is shown restoring parts of this historic symbol of a cultural civilization. ]]> http://antwrp.gsfc.nasa.gov/apod/ap090620.html Sat, 20 Jun 2009 13:06:00 GMT This surprising view of the Full Moon rising on June 7 was captured with a telephoto lens from a seaside balcony near Nice, France. The orange Moon's dark markings and odd shape put the photographer in mind of an alien creature's face staring down at the passing ship. Of course, the Moon's distorted appearance is due to the unusual bending (refraction) of light rays creating multiple images or mirages, similar to sunset and sunrise mirages. The effects are most pronounced when temperature layers in the atmosphere produce sharp changes in air density and refractive index. Acting over long sight-lines to the rising and setting Sun or Moon, the refraction significantly alters the path of light rays creating merged, distorted images. Such mirages are also associated with the Green Flash. ]]> http://antwrp.gsfc.nasa.gov/apod/ap090619.html Fri, 19 Jun 2009 13:06:01 GMT This ancient Chinese map of planet Earth's northern sky is part of the Dunhuang Star Atlas, one of the most impressive documents in the history of astronomy. The oldest complete star atlas known, it dates to the years 649 to 684, discovered at the Silk Road town of Dunhuang in 1907. A recent analysis that examines the accuracy and projections used to make it notes the atlas marks positions of over 1,300 stars and outlines 257 Chinese star groups or asterisms. The star positions in the hand drawn atlas were found to be accurate to within a few degrees. In this example showing the north polar region, a very recognizable Big Dipper, part of the modern constellation Ursa Major, lies along the bottom of the chart. An additional 12 charts depict equatorial regions in 30 degree sections and also include a grouping resembling the modern constellation Orion. The atlas is on display at the British Library in London to celebrate the International Year of Astronomy. ]]> http://antwrp.gsfc.nasa.gov/apod/ap090618.html Thu, 18 Jun 2009 13:06:00 GMT NGC 6240 offers a rare glimpse of a cosmic catastrophe in its final throes. The titanic galaxy-galaxy collision is located a mere 400 million light-years away in the constellation Ophiuchus. One of the brightest sources in the infrared sky, the merging galaxies spew distorted tidal tails of stars, gas, and dust and undergo frantic bursts of star formation. The two supermassive black holes in the original galactic cores will also coalesce into a single, even more massive black hole. Soon, only one large galaxy will remain. This dramatic image of the scene is a multiwavelength composite; red colors trace infrared emission from dust recorded by the Spitzer Space Telescope, with Hubble visible light images of stars and gas in green and blue hues. The view spans over 300,000 light-years at the estimated distance of NGC 6240. ]]> http://antwrp.gsfc.nasa.gov/apod/ap090617.html Wed, 17 Jun 2009 13:06:01 GMT M13 is one of the most prominent and best known globular clusters. Visible with binoculars in the constellation of Hercules, M13 is frequently one of the first objects found by curious sky gazers seeking celestials wonders beyond normal human vision. M13 is a colossal home to over 100,000 stars, spans over 150 light years across, lies over 20,000 light years distant, and is over 12 billion years old. At the 1974 dedication of Arecibo Observatory, a radio message about Earth was sent in the direction of M13. The reason for the low abundance of unusual blue straggler stars in M13 is remains unknown. ]]> http://antwrp.gsfc.nasa.gov/apod/ap090616.html Tue, 16 Jun 2009 13:06:01 GMT Is the Moon larger when near the horizon? No -- as shown above, the Moon appears to be very nearly the same size no matter its location on the sky. Oddly, the cause or causes for the common Moon Illusion are still being debated. Two leading explanations both hinge on the illusion that foreground objects make a horizon Moon seem farther in the distance. The historically most popular explanation then holds that the mind interprets more distant objects as wider, while a more recent explanation adds that the distance illusion may actually make the eye focus differently. Either way, the angular diameter of the Moon is always about 0.5 degrees. In the above time-lapse sequence of the Moon taken in 2007, with one exposure taken to bring up the foreground of Izmit Bay in Turkey. On the occasion of our 14th anniversary, the APOD editors thank all of our contributors and mirror site operators whose volunteer efforts help bring the wonders of astronomy to millions of people around the world. Additional thanks also go to our Turkish mirror site operators for submitting the above mouseover image. ]]> http://antwrp.gsfc.nasa.gov/apod/ap090615.html Mon, 15 Jun 2009 13:06:01 GMT Dark dust lit by the bright yellow star Antares highlight this photogenic starscape of the southern sky. A wider angle image shows the central band of our Milky Way Galaxy connected to Antares by streams of dust knows as the Dark River. At the head of the Dark River the dust appears in dense knots. One of the densest knots is B44, pictured near the bottom of the above image. Off to the left of the above image lies Antares, a star so bright that the pictured dust reflects its light, giving it a distinct yellow hue. Light from the blue star on the image left creates a surrounding blue reflection nebula named IC 4605. B44 and IC 4605 lies about 500 light years distant toward the constellation of the Scorpion. ]]> http://antwrp.gsfc.nasa.gov/apod/ap090614.html Sun, 14 Jun 2009 13:06:01 GMT The center of our Milky Way Galaxy is hidden from the prying eyes of optical telescopes by clouds of obscuring dust and gas. But in this stunning vista, the Spitzer Space Telescope's infrared cameras, penetrate much of the dust revealing the stars of the crowded galactic center region. A mosaic of many smaller snapshots, the detailed, false-color image shows older, cool stars in bluish hues. Reddish glowing dust clouds are associated with young, hot stars in stellar nurseries. The very center of the Milky Way was only recently found capable of forming newborn stars. The galactic center lies some 26,000 light-years away, toward the constellation Sagittarius. At that distance, this picture spans about 900 light-years. ]]> http://antwrp.gsfc.nasa.gov/apod/ap090613.html Sat, 13 Jun 2009 13:06:01 GMT Inspired by the night skies of planet Earth in the International Year of Astronomy, photographer Larry Landolfi created this tantalizing fantasy view. The composited image suggests a luminous Milky Way is the heavenly extension of a country road. Of course, the name for our galaxy, the Milky Way (in Latin, Via Lactea), does refer to its appearance as a milky band or path in the sky. In fact, the word galaxy itself derives from the Greek for milk. Visible on moonless nights from dark sky areas, though not so bright or colorful as in this image, the glowing celestial band is due to the collective light of myriad stars along the plane of our galaxy, too faint to be distinguished individually. The diffuse starlight is cut by dark swaths of obscuring galactic dust clouds. Four hundred years ago, Galileo turned his telescope on the Milky Way and announced it to be "... a congeries of innumerable stars ..." ]]> http://antwrp.gsfc.nasa.gov/apod/ap090612.html Fri, 12 Jun 2009 13:06:01 GMT SNR 0104 is a supernova remnant with an unusual shape. Found 190,000 light-years away in our neighboring galaxy the Small Magellanic Cloud, SNR 0104 is suspected of being the expanding debris cloud from a Type 1a supernova - the catastrophic thermonuclear explosion of a white dwarf star. For example, like Type 1a supernova remnants within our galaxy, investigations show that it contains large amounts of iron. But unlike other Type 1a remnants, including the well-studied Tycho, Kepler, and SN 1006, SNR 0104 is definitely not spherical. In fact, the remnant's shape suggests this supernova explosion was very asymmetric and produced strong jets. This intriguing composite image combines Chandra Observatory x-ray data of the remnant, shown in purple hues, with Spitzer Space Telescope infrared data covering the wider region, mapped to red and green colors. It indicates that the supernova explosion took place in the complicated and dense environment of a star-forming region. So, an alternative explanation is that the expanding debris cloud is sweeping up clumpy interstellar material, accounting for the odd shape of SNR 0104. The broad, multiwavelength view spans about 1,800 light-years at the estimated distance of SNR 0104. ]]>