Astronomy Picture of the Day (General/Chat)
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Explanation: Sometimes the dark dust of interstellar space has an angular elegance. Such is the case toward the far-south constellation of Chamaeleon. Normally too faint to see, dark dust is best known for blocking visible light from stars and galaxies behind it. In this 36.6-hour exposure, however, the dust is seen mostly in light of its own, with its strong red and near-infrared colors creating a brown hue. Contrastingly blue, the bright star Beta Chamaeleontis is visible on the upper right, with the dust that surrounds it preferentially reflecting blue light from its primarily blue-white color. All of the pictured...
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Explanation: This rock structure is not only surreal -- it's real. Perhaps the reason it's not more famous is that it is smaller than one might guess: the capstone rock overhangs only a few meters. Even so, the King of Wings outcrop, located in New Mexico, USA, is a fascinating example of an unusual type of rock structure called a hoodoo. Hoodoos may form when a layer of hard rock overlays a layer of eroding softer rock. Figuring out the details of incorporating this hoodoo into a night-sky photoshoot took over a year. Besides waiting for a suitably picturesque night...
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Explanation: Have you seen a panorama from another world lately? Assembled from high-resolution scans of the original film frames, this one sweeps across the magnificent desolation of the Apollo 11 landing site on the Moon's Sea of Tranquility. The images were taken 55 years ago by Neil Armstrong looking out his window on the Eagle Lunar Module shortly after the July 20, 1969 landing. The frame at the far left (AS11-37-5449) is the first picture taken by a person on another world. Thruster nozzles can be seen in the foreground on the left (toward the south), while at the right...
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Explanation: For some, these subtle bands of light and shadow stretched across the sky as the Sun set on July 11. Known as anticrepuscular rays, the bands are formed as a large cloud bank near the western horizon cast long shadows through the atmosphere at sunset. Due to the camera's perspective, the bands of light and shadow seem to converge toward the eastern (opposite) horizon at a point seen just above a 14th century hilltop castle in Brno, Czech Republic. In the foreground, denizens of planet Earth are enjoying the region's annual Planet Festival in the park below the Brno...
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Explanation: Unlike most entries in Charles Messier's famous catalog of deep sky objects, M24 is not a bright galaxy, star cluster, or nebula. It's a gap in nearby, obscuring interstellar dust clouds that allows a view of the distant stars in the Sagittarius spiral arm of our Milky Way galaxy. Direct your gaze through this gap with binoculars or small telescope and you are looking through a window over 300 light-years wide at stars some 10,000 light-years or more from Earth. Sometimes called the Small Sagittarius Star Cloud, M24's luminous stars are left of center in this gorgeous starscape. Covering...
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Explanation: When Vulcan, the Roman god of fire, swings his blacksmith's hammer, the sky is lit on fire. A recent eruption of Chile's Villarrica volcano shows the delicate interplay between this fire -- actually glowing steam and ash from melted rock -- and the light from distant stars in our Milky Way galaxy and the Magellanic Clouds galaxies. In the featured timelapse video, the Earth rotates under the stars as Villarrica erupts. With about 1350 volcanoes, our planet Earth rivals Jupiter's moon Io as the most geologically active place in the Solar System. While both have magnificent beauty, the reasons...
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Explanation: What are these unusual interstellar structures? Bright-rimmed, flowing shapes gather near the center of this rich starfield toward the borders of the nautical southern constellations Pupis and Vela. Composed of interstellar gas and dust, the grouping of light-year sized cometary globules is about 1300 light-years distant. Energetic ultraviolet light from nearby hot stars has molded the globules and ionized their bright rims. The globules also stream away from the Vela supernova remnant which may have influenced their swept-back shapes. Within them, cores of cold gas and dust are likely collapsing to form low mass stars, whose formation will ultimately...
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Explanation: Why does this galaxy have such a long tail? In this stunning vista, based on image data from the Hubble Legacy Archive, distant galaxies form a dramatic backdrop for disrupted spiral galaxy Arp 188, the Tadpole Galaxy. The cosmic tadpole is a mere 420 million light-years distant toward the northern constellation of the Dragon (Draco). Its eye-catching tail is about 280 thousand light-years long and features massive, bright blue star clusters. One story goes that a more compact intruder galaxy crossed in front of Arp 188 - from right to left in this view - and was slung around...
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Explanation: The galaxy was never in danger. For one thing, the Triangulum galaxy (M33), pictured, is much bigger than the tiny grain of rock at the head of the meteor. For another, the galaxy is much farther away -- in this instance 3 million light years as opposed to only about 0.0003 light seconds. Even so, the meteor's path took it angularly below the galaxy. Also the wind high in Earth's atmosphere blew the meteor's glowing evaporative molecule train away from the galaxy, in angular projection. Still, the astrophotographer was quite lucky to capture both a meteor and a galaxy...
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Explanation: In 1990, cruising four billion miles from the Sun, the Voyager 1 spacecraft looked back to make this first ever Solar System family portrait. The complete portrait is a 60 frame mosaic made from a vantage point 32 degrees above the ecliptic plane. In it, Voyager's wide-angle camera frames sweep through the inner Solar System at the left, linking up with ice giant Neptune, the Solar System's outermost planet, at the far right. Positions for Venus, Earth, Jupiter, Saturn, Uranus, and Neptune are indicated by letters, while the Sun is the bright spot near the center of the circle...
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Explanation: Planetary nebula Jones-Emberson 1 is the death shroud of a dying Sun-like star. It lies some 1,600 light-years from Earth toward the sharp-eyed constellation Lynx. About 4 light-years across, the expanding remnant of the dying star's atmosphere was shrugged off into interstellar space, as the star's central supply of hydrogen and then helium for fusion was depleted after billions of years. Visible near the center of the planetary nebula is what remains of the stellar core, a blue-hot white dwarf star. Also known as PK 164 +31.1, the nebula is faint and very difficult to glimpse at a telescope's...
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Explanation: Globular star cluster Omega Centauri packs about 10 million stars much older than the Sun into a volume some 150 light-years in diameter. Also known as NGC 5139, at a distance of 15,000 light-years it's the largest and brightest of 200 or so known globular clusters that roam the halo of our Milky Way galaxy. Though most star clusters consist of stars with the same age and composition, the enigmatic Omega Cen exhibits the presence of different stellar populations with a spread of ages and chemical abundances. In fact, Omega Cen may be the remnant core of a small...
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Explanation: These three bright nebulae are often featured on telescopic tours of the constellation Sagittarius and the crowded starfields of the central Milky Way. In fact, 18th century cosmic tourist Charles Messier cataloged two of them; M8, the large nebula above center, and colorful M20 below and left in the frame. The third emission region includes NGC 6559, right of M8 and separated from the larger nebula by a dark dust lane. All three are stellar nurseries about five thousand light-years or so distant. Over a hundred light-years across the expansive M8 is also known as the Lagoon Nebula. M20's...
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Explanation: These clouds are doubly unusual. First, they are rare noctilucent clouds, meaning that they are visible at night -- but only just before sunrise or just after sunset. Second, the source of these noctilucent clouds is actually known. In this rare case, the source of the sunlight-reflecting ice-crystals in the upper atmosphere can be traced back to the launch of a nearby SpaceX rocket about 30 minutes earlier. Known more formally as polar mesospheric clouds, the vertex of these icy wisps happens to converge just in front of a rising crescent Moon. The featured image -- and accompanying video...
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Explanation: Why are these clouds multi-colored? A relatively rare phenomenon in clouds known as iridescence can bring up unusual colors vividly -- or even a whole spectrum of colors simultaneously. These polar stratospheric clouds also, known as nacreous and mother-of-pearl clouds, are formed of small water droplets of nearly uniform size. When the Sun is in the right position and, typically, hidden from direct view, these thin clouds can be seen significantly diffracting sunlight in a nearly coherent manner, with different colors being deflected by different amounts. Therefore, different colors will come to the observer from slightly different directions. Many...
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Explanation: Found among the rich starfields of the Milky Way, star cluster NGC 7789 lies about 8,000 light-years away toward the constellation Cassiopeia. A late 18th century deep sky discovery of astronomer Caroline Lucretia Herschel, the cluster is also known as Caroline's Rose. Its visual appearance in small telescopes, created by the cluster's complex of stars and voids, is suggestive of nested rose petals. Now estimated to be 1.6 billion years young, the galactic or open cluster of stars also shows its age. All the stars in the cluster were likely born at the same time, but the brighter and...
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Explanation: A glow from the summit of Mount Etna, famous active stratovolcano of planet Earth, stands out along the horizon in this mountain and night skyscape. Bands of diffuse light from congeries of innumerable stars along the Milky Way galaxy stretch across the sky above. In silhouette, the Milky Way's massive dust clouds are clumped along the galactic plane. Also familiar to northern skygazers are bright stars Deneb, Vega, and Altair, the Summer Triangle straddling dark nebulae and luminous star clouds poised over the volcanic peak. The deep combined exposures reveal the light of active star forming regions along the...
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Explanation: The beautiful Trifid Nebula is a cosmic study in contrasts. Also known as M20, it lies about 5,000 light-years away toward the nebula rich constellation Sagittarius. A star forming region in the plane of our galaxy, the Trifid does illustrate three different types of astronomical nebulae; red emission nebulae dominated by light from hydrogen atoms, blue reflection nebulae produced by dust reflecting starlight, and dark nebulae where dense dust clouds appear in silhouette. But the red emission region, roughly separated into three parts by obscuring dust lanes, is what lends the Trifid its popular name. Pillars and jets sculpted...
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Explanation: Big, bright, and beautiful, spiral galaxy M83 lies a mere twelve million light-years away, near the southeastern tip of the very long constellation Hydra. About 40,000 light-years across, M83 is known as the Southern Pinwheel for its pronounced spiral arms. But the wealth of reddish star forming regions found near the edges of the arms' thick dust lanes, also suggest another popular moniker for M83, the Thousand-Ruby Galaxy. This new deep telescopic digital image also records the bright galaxy's faint, extended halo. Arcing toward the bottom of the cosmic frame lies a stellar tidal stream, debris drawn from massive...
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Explanation: The clouds may look like an oyster, and the stars like pearls, but look beyond. Near the outskirts of the Small Magellanic Cloud, a satellite galaxy some 200 thousand light-years distant, lies this 5 million year old star cluster NGC 602. Surrounded by its birth shell of gas and dust, star cluster NGC 602 is featured in this stunning Hubble image, augmented in a rollover by images in the X-ray by the Chandra Observatory and in the infrared by Spitzer Telescope. Fantastic ridges and swept back gas strongly suggest that energetic radiation and shock waves from NGC 602's massive...
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