Astronomy Picture of the Day

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Discover the cosmos! Each day a different image or photograph of our fascinating universe is featured, along with a brief explanation written by a professional astronomer.
2010 July 15

Andes Sunset Eclipse
Credit & Copyright: Janne Pyykkö Explanation: On July 11, after a long trek eastward across the southern Pacific Ocean, the Moon's shadow reached landfall in South America. In a total solar eclipse close to sunset, silhouetted Moon and Sun hugged the western horizon, seen here above the Andes mountains near the continent's southern tip. To enjoy a good vantage point, the photographer hiked to a windy spot about 400 meters above a lake, Lago Argentino, climbing into the picture after setting up his camera on a tripod. At left, the sky outside the shadow cone is still bright. Below, the lights of El Calafate, Patagonia, Argentina, shine by the lake shore.

 

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Discover the cosmos! Each day a different image or photograph of our fascinating universe is featured, along with a brief explanation written by a professional astronomer.
2010 July 16

Shaping NGC 6188
Credit & Copyright: Piotrek Sadowski Explanation: Dark shapes with bright edges winging their way through dusty NGC 6188 are tens of light-years long. The emission nebula is found near the edge of an otherwise dark large molecular cloud in the southern constellation Ara, about 4,000 light-years away. Formed in that region only a few million years ago, the massive young stars of the embedded Ara OB1 association sculpt the fantastic shapes and power the nebular glow with stellar winds and intense ultraviolet radiation. The recent star formation itself was likely triggered by winds and supernova explosions, from previous generations of massive stars, that swept up and compressed the molecular gas. A false-color Hubble palette was used to create the this sharp close-up image and shows emission from sulfur, hydrogen, and oxygen atoms in red, green, and blue hues. At the estimated distance of NGC 6188, the picture spans about 200 light-years.

 

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Discover the cosmos! Each day a different image or photograph of our fascinating universe is featured, along with a brief explanation written by a professional astronomer.
2010 August 31

The Annotated Galactic Center
Credit & Copyright: Jamie Fernandez Explanation: The sky toward the center of our Galaxy is filled with a wide variety of celestial wonders, many of which are visible from a dark location with common binoculars. Constellations near the Galactic Center include Sagittarius, Libra, Scorpius, Scutum, and Ophiuchus. Nebulas include Messier objects M8, M16, M20, as well as the Pipe and Cat's Paw nebulas. Visible open star clusters include M6, M7, M21, M23, M24, and M25, while globular star cluster M22 is also visible. A hole in the dust toward the Galactic Center reveals a bright region filled with distant stars known as Baade's Window, which is visible between M7 and M8. Moving your cursor over the above image the will bring up an un-annotated version.

 

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Discover the cosmos! Each day a different image or photograph of our fascinating universe is featured, along with a brief explanation written by a professional astronomer.
2010 September 1

Earth and Moon from MESSENGER
Credit: NASA/JHU APL/CIW Explanation: What does Earth look like from the planet Mercury? The robotic spacecraft MESSENGER found out as it looked toward the Earth during its closest approach to the Sun about three months ago. The Earth and Moon are visible as the double spot on the lower left of the above image. Now MESSENGER was not at Mercury when it took the above image, but at a location from which the view would be similar. From Mercury, both the Earth and its comparatively large moon will always appear as small circles of reflected sunlight and will never show a crescent phase. MESSENGER has zipped right by Mercury three times since being launched in 2004, and is scheduled to enter orbit around the innermost planet in March of 2011.

 

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2010 September 2

The Bubble Nebula
Credit & Copyright: Dave Jurasevich (Mount Wilson Observatory)
Explanation: Blown by the wind from a massive star, this interstellar apparition has a surprisingly familiar shape. Cataloged as NGC 7635, it is also known simply as The Bubble Nebula. Although it looks delicate, the 10 light-year diameter bubble offers evidence of violent processes at work. Above and right of the Bubble's center is a hot, O-type star, several hundred thousand times more luminous and approximately 45 times more massive than the Sun. A fierce stellar wind and intense radiation from that star has blasted out the structure of glowing gas against denser material in a surrounding molecular cloud. The intriguing Bubble Nebula lies a mere 11,000 light-years away toward the boastful constellation Cassiopeia. A false-color Hubble palette was used to create this sharp image and shows emission from sulfur, hydrogen, and oxygen atoms in red, green, and blue hues. The image data was recorded using a small telescope under clear, steady skies, from Mount Wilson Observatory.

 

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Discover the cosmos! Each day a different image or photograph of our fascinating universe is featured, along with a brief explanation written by a professional astronomer.
2010 September 3

The Small Cloud of Magellan
Credit & Copyright: Bogdan Jarzyna
Explanation: Portuguese navigator Ferdinand Magellan and his crew had plenty of time to study the southern sky during the first circumnavigation of planet Earth. As a result, two celestial wonders easily visible for southern hemisphere skygazers are known as the Clouds of Magellan. These cosmic clouds are now understood to be dwarf irregular galaxies, satellites of our larger spiral Milky Way Galaxy. The Small Magellanic Cloud actually spans 15,000 light-years or so and contains several hundred million stars. About 210,000 light-years away in the constellation Tucana, it is more distant than other known Milky Way satellite galaxies, including the Canis Major and Sagittarius Dwarf galaxies and the Large Magellanic Cloud. This sharp image also includes two foreground globular star clusters NGC 362 (bottom right) and 47 Tucanae. Spectacular 47 Tucanae is a mere 13,000 light-years away and seen here to the left of the Small Magellanic Cloud.

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Discover the cosmos! Each day a different image or photograph of our fascinating universe is featured, along with a brief explanation written by a professional astronomer.
2010 September 4

Young Suns of NGC 7129
Credit & Copyright: Ken Crawford (Rancho Del Sol Obs.)
Explanation: Young suns still lie within dusty NGC 7129, some 3,000 light-years away toward the royal constellation Cepheus. While these stars are at a relatively tender age, only a few million years old, it is likely that our own Sun formed in a similar stellar nursery some five billion years ago. Most noticeable in the sharp, (zoomable) image are the lovely bluish dust clouds that reflect the youthful starlight, but the smaller, deep red crescent shapes are also markers of energetic, young stellar objects. Known as Herbig-Haro objects, their shape and color is characteristic of glowing hydrogen gas shocked by jets streaming away from newborn stars. Ultimately the natal gas and dust in the region will be dispersed, the stars drifting apart as the loose cluster orbits the center of the Galaxy. At the estimated distance of NGC 7129, this telescopic view spans about 40 light-years.

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Discover the cosmos! Each day a different image or photograph of our fascinating universe is featured, along with a brief explanation written by a professional astronomer.
2010 September 5

GRO J1655-40: Evidence for a Spinning Black Hole
Credit: April Hobart, CXC Explanation: In the center of a swirling whirlpool of hot gas is likely a beast that has never been seen directly: a black hole. Studies of the bright light emitted by the swirling gas frequently indicate not only that a black hole is present, but also likely attributes. The gas surrounding GRO J1655-40, for example, has been found to display an unusual flickering at a rate of 450 times a second. Given a previous mass estimate for the central object of seven times the mass of our Sun, the rate of the fast flickering can be explained by a black hole that is rotating very rapidly. What physical mechanisms actually cause the flickering -- and a slower quasi-periodic oscillation (QPO) -- in accretion disks surrounding black holes and neutron stars remains a topic of much research.

 

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Discover the cosmos! Each day a different image or photograph of our fascinating universe is featured, along with a brief explanation written by a professional astronomer.
2010 September 6

A Laser Strike at the Galactic Center
Credit: Yuri Beletsky (ESO) Explanation: Why are these people shooting a powerful laser into the center of our Galaxy? Fortunately, this is not meant to be the first step in a Galactic war. Rather, astronomers at the Very Large Telescope (VLT) site in Chile are trying to measure the distortions of Earth's ever changing atmosphere. Constant imaging of high-altitude atoms excited by the laser -- which appear like an artificial star -- allow astronomers to instantly measure atmospheric blurring. This information is fed back to a VLT telescope mirror which is then slightly deformed to minimize this blurring. In this case, a VLT was observing our Galaxy's center, and so Earth's atmospheric blurring in that direction was needed. As for inter-galaxy warfare, when viewed from our Galaxy's center, no casualties are expected. In fact, the light from this powerful laser would combine with light from our Sun to together appear only as bright as a faint and distant star.

 

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Discover the cosmos! Each day a different image or photograph of our fascinating universe is featured, along with a brief explanation written by a professional astronomer.
2010 September 7

Space Shuttle Tribute Poster: Endeavour
Credit: NASA Explanation: They are some of the most complex machines ever built. From a standing start they can launch a school- bus sized object up so high and moving so fast that it won't fall back down. They have launched numerous revolutionary satellites that enable humans to communicate across the globe, to better understand Earth's atmosphere, and to peer into the distance universe. They are NASA's Space Shuttles, and NASA has recently released large digital posters to honor them. While the inaugural flight was in 1981, the shuttle fleet is aging and is now nearing retirement. Pictured above, the space shuttle Endeavour is shown rising to orbit, with patches for each of its missions shown in a spiral. Endeavour was named for the HMS Endeavour, a British research ship that explored the south Pacific Ocean in the 1700s, depicted on the lower right. On the upper left are panoramic windows delivered by Endeavour to the International Space Station earlier this year. In the background near the top is the NGC 602 nebula as imaged by the Hubble Space Telescope, which was serviced by Endeavour in 1993. Posters for all of the shuttles, including Atlantis, Challenger, Columbia, Discovery, Endeavour are available.

 

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2010 September 8

NGC 4911: Spiral Diving into a Dense Cluster
Credit: NASA, ESA, and the Hubble Heritage Team (STScI/AURA); Acknowledgment: K. Cook (LLNL) et al. Explanation: Why are there faint rings around this spiral galaxy? Possibly because the galaxy, NGC 4911, is being pulled at by its neighbors as it falls into the enormous Coma Cluster of Galaxies. If NGC 4911 ends up like most of the galaxies in the central Coma cluster, it will become a yellowish elliptical galaxy, losing not only its outer layers, but dust, gas, and its cadre of surrounding satellite galaxies as well. Currently, however, this process is just beginning. Visible in the above deep image from the Hubble Space Telescope are NGC 4911's bright nucleus, distorted spiral arms laced with dark dust, clusters of recently formed stars, unusual faint outer rings, dwarf companion galaxies, and even faint globular clusters of stars. Far in the distance many unassociated galaxies from the early universe are visible, some even through NGC 4911 itself. The Coma Cluster contains over 1,000 galaxies making it among the most massive objects known. NGC 4911 can be found to the lower left of the great cluster's center.

 

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2010 September 9

Cepheus: Trunk to Bubble
Credit & Copyright: Rogelio Bernal Andreo
Explanation: Star clusters, glowing nebulae and dark dust clouds abound in Cepheus, royal constellation of the northern hemisphere. You can follow them in amazing detail across this broad skyscape, a mosaic of telescopic images spanning about 17 degrees. Beginning at the lower left, the large emission nebula is cataloged as IC 1396. Hundreds of light-years across and about 3,000 light-years distant, it contains a dark, winding, tendril-shaped feature popularly known as the Elephant's Trunk. Near the top middle, the bright nebula with an embedded star cluster is NGC 7380. At the upper right lies NGC 7635 (the Bubble Nebula) and star cluster M52. Put your cursor over the picture to see a labeled version of the field. Many of the objects highlighted have a designation from the second version of the Sharpless catalog (Sh2) and the Barnard catalog (B) of dark nebulae. Associated with star formation, the sites are telltale markers along the region's complex of giant molecular clouds.

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2010 September 10

Vela Supernova Remnant
Credit & Copyright: Marco Lorenzi (Star Echoes)
Explanation: The plane of our Milky Way Galaxy runs through this complex and beautiful skyscape. At the northwestern edge of the constellation Vela (the Sails) the four frame mosaic is over 10 degrees wide, centered on the glowing filaments of the Vela Supernova Remnant, the expanding debris cloud from the death explosion of a massive star. Light from the supernova explosion that created the Vela remnant reached Earth about 11,000 years ago. In addition to the shocked filaments of glowing gas, the cosmic catastrophe also left behind an incredibly dense, rotating stellar core, the Vela Pulsar. Some 800 light-years distant, the Vela remnant is likely embedded in a larger and older supernova remnant, the Gum Nebula.

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2010 September 11

Star Streams and the Sunflower Galaxy
Image Credit & Copyright: R Jay GaBany - Collaboration: T.S. Chonis (U. Texas),
D. Martinez-Delgado (MPIA, IAC), Ray Gralak (New Mexico Skies), Gary J. Hill (McDonald Obs), I. Trujillo (IAC), S. R. Majewski (U. Virginia)
Explanation: A bright spiral galaxy of the northern sky, Messier 63 is about 25 million light-years distant in the loyal constellation Canes Venatici. Also cataloged as NGC 5055, the majestic island universe is nearly 100,000 light-years across, about the size of our own Milky Way. Known by the popular moniker, The Sunflower Galaxy, M63 sports a bright yellowish core and sweeping blue spiral arms, streaked with cosmic dust lanes and dotted with pink star forming regions. This deep exposure also reveals an enormous but dim arc extending far into the halo above the brighter galactic plane. A collaboration of professional and amateur astronomers has shown the arc to be consistent with the stellar stream from a smaller satellite galaxy, tidally disrupted as it merged with M63 during the last 5 billion years. Their discovery is part of an increasing body of evidence that the growth of large spirals by cannibalizing smaller galaxies is commonplace in the nearby Universe.

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Discover the cosmos! Each day a different image or photograph of our fascinating universe is featured, along with a brief explanation written by a professional astronomer.
2010 September 12

Oklo: Ancient African Nuclear Reactors
Credit & Copyright: Robert D. Loss (Curtin U.) Explanation: The remnants of nuclear reactors nearly two billion years old were found in the 1970s in Africa. These reactors are thought to have occurred naturally. No natural reactors exist today, as the relative density of fissile uranium has now decayed below that needed for a sustainable reaction. Pictured above is Fossil Reactor 15, located in Oklo, Gabon. Uranium oxide remains are visible as the yellowish rock. Oklo by-products are being used today to probe the stability of the fundamental constants over cosmological time and distance scales and to develop more effective means for disposing of human-manufactured nuclear waste.

 

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2010 September 13

Zodiacal Light Over Namibia
Credit & Copyright: Rudi Dobesberger (Sternfreunde Steyr) Explanation: An unusual triangle of light is visible this time of year just before dawn, in the northern hemisphere. Once considered a false dawn, this triangle of light is actually zodiacal light, light reflected from interplanetary dust particles. The bright reflecting triangle is clearly visible on the right of the above horizontally-compressed image taken just after sunset from Namibia in the southern hemisphere in 2009 June. The central band of our Milky Way Galaxy on the left first mirrors the zodiacal band on the right but then curves around the sky. The faint smudges inside the arch of the Milky Way are the Large and Small Magellanic Clouds. Zodiacal dust orbits the Sun predominantly in the same plane as the planets: the ecliptic. Zodiacal light is so bright in the north this time of year because the dust band is oriented nearly vertical at sunrise, so that the thick air near the horizon does not block out relatively bright reflecting dust. Zodiacal light is also bright for people in Earth's northern hemisphere in March and April just after sunset. In the southern hemisphere, zodiacal light is most notable after sunset in late summer, and brightest before sunrise in late spring.

 

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Discover the cosmos! Each day a different image or photograph of our fascinating universe is featured, along with a brief explanation written by a professional astronomer.
2010 September 14

An Extraordinary Spiral from LL Pegasi
Credit: ESA, Hubble, R. Sahai (JPL), NASA Explanation: What created the strange spiral structure on the left? No one is sure, although it is likely related to a star in a binary star system entering the planetary nebula phase, when its outer atmosphere is ejected. The huge spiral spans about a third of a light year across and, winding four or five complete turns, has a regularity that is without precedent. Given the expansion rate of the spiral gas, a new layer must appear about every 800 years, a close match to the time it takes for the two stars to orbit each other. The star system that created it is most commonly known as LL Pegasi, but also AFGL 3068. The unusual structure itself has been cataloged as IRAS 23166+1655. The above image was taken in near-infrared light by the Hubble Space Telescope. Why the spiral glows is itself a mystery, with a leading hypothesis being illumination by light reflected from nearby stars.

 

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2010 September 15

Clouds, Birds, Moon, Venus
Credit & Copyright: Isaac Gutiérrez Pascual (Spain) Explanation: Sometimes the sky above can become quite a show. Last week, for example, the Moon and Venus converged, creating quite a sight by itself for sky enthusiasts around the globe. From some locations, though, the sky was even more picturesque. In the above image taken last week from Spain, a crescent Moon and the planet Venus, on the far right, were captured during sunset posing against a deep blue sky. In the foreground, dark storm clouds loom across the image bottom, while a white anvil cloud shape appears above. Black specks dot the frame, caused by a flock of birds taking flight. Very soon after this picture was taken, however, the birds passed by, the storm ended, and Venus and the Moon set. The Moon and Venus have now separated, although Venus will remain visible at sunset for the rest of this month.

 

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2010 September 16

The Veil Nebula
Credit & Copyright: Martin Pugh
Explanation: Delicate in appearance, these filaments of shocked, glowing gas, draped in planet Earth's sky toward the constellation of Cygnus, make up the Veil Nebula. The nebula is a large supernova remnant, an expanding cloud born of the death explosion of a massive star. Light from the original supernova explosion likely reached Earth over 5,000 years ago. Also known as the Cygnus Loop, the Veil Nebula now spans nearly 3 degrees or about 6 times the diameter of the full Moon. That translates to over 70 light-years at its estimated distance of 1,500 light-years. In fact, the Veil is so large its brighter parts are recognized as separate nebulae, including The Witch's Broom (NGC 6960) at the bottom of this stunning skyview and Pickering's Triangle (NGC 6979) below and right of center. At the top is the haunting IC 1340.

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Discover the cosmos! Each day a different image or photograph of our fascinating universe is featured, along with a brief explanation written by a professional astronomer.
2010 September 17

Northern Lights over Prelude Lake
Image Credit & Copyright: Yuichi Takasaka / TWAN / www.blue-moon.ca
Explanation: Curtains of shimmering green light sprawl across this gorgeous night skyscape. In the foreground lies the peaceful Prelude Lake, located about 30 kilometers east of Yellowknife, Northwest Territories, Canada. From high northern latitudes these mesmerizing northern lights, also known as the aurora borealis, are becoming a more familiar sight. As the September 23rd equinox approaches, nights grow longer and a favorable season for aurora begins. Recorded on September 11, this panoramic scene spans about 180 degrees. Brighter stars peering through the auroral glow at the left form the recognizable northern asterism, the Big Dipper. A more compact Pleiades star cluster shines at the far right.

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