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Explanation: What lights up this castle of star formation? The familiar Eagle Nebula glows bright in many colors at once. The above image is a composite of three of these glowing gas colors. Pillars of dark dust nicely outline some of the denser towers of star formation. Energetic light from young massive stars causes the gas to glow and effectively boils away part of the dust and gas from its birth pillar. Many of these stars will explode after several million years, returning most of their elements back to the nebula which formed them. This process is forming an open...

Explanation: This fifteen degree wide field of view stretches across the crowded starfields of Sagittarius toward the center of our Milky Way galaxy. In fact, the center of the galaxy lies near the right edge of the rich starscape and eleven bright star clusters and nebulae fall near the center of the frame. All eleven are numbered entries in the catalog compiled by 18th century cosmic tourist Charles Messier. Gaining celebrity status with skygazers, M8 (Lagoon), M16 (Eagle), M17 (Omega), and M20 (Trifid) show off the telltale reddish hues of emission nebulae associated with star forming regions. But also eye-catching...

Explanation: Beautiful barred spiral galaxy M109, 109th entry in Charles Messier's famous catalog of bright Nebulae and Star Clusters, is found just below the Big Dipper's bowl in the northern constellation Ursa Major. In telescopic views, its striking central bar gives the galaxy the appearance of the Greek letter "theta", θ, a common mathematical symbol representing an angle. Of course M109 spans a very small angle in planet Earth's sky, about 7 arcminutes or 0.12 degrees. But that small angle corresponds to an enormous 120,000 light-year diameter at the galaxy's estimated 60 million light-year distance. The brightest member of the...

Explanation: Face-on spiral galaxy M77 lies a mere 47 million light-years away toward the aquatic constellation Cetus. At that estimated distance, the gorgeous island universe is about 100 thousand light-years across. Also known as NGC 1068, its compact and very bright core is well studied by astronomers exploring the mysteries of supermassive black holes in active Seyfert galaxies. M77 is also seen at x-ray, ultraviolet, infrared, and radio wavelengths. But this sharp visible light image based on Hubble data follows its winding spiral arms traced by obscuring dust clouds and red-tinted star forming regions close in to the galaxy's luminous...

Explanation: Sculpted by stellar winds and radiation, the star factory known as Messier 17 lies some 5,500 light-years away in the nebula-rich constellation Sagittarius. At that distance, this degree wide field of view spans almost 100 light-years. The sharp, composite, color image utilizing data from space and ground based telescopes, follows faint details of the region's gas and dust clouds against a backdrop of central Milky Way stars. Stellar winds and energetic light from hot, massive stars formed from M17's stock of cosmic gas and dust have slowly carved away at the remaining interstellar material producing the cavernous appearance and...

Explanation: One of the brightest galaxies in planet Earth's sky is similar in size to our Milky Way Galaxy: big, beautiful M81. This grand spiral galaxy lies 11.8 million light-years away toward the northern constellation of the Great Bear (Ursa Major). The deep image of the region reveals details in the bright yellow core, but at the same time follows fainter features along the galaxy's gorgeous blue spiral arms and sweeping dust lanes. It also follows the expansive, arcing feature, known as Arp's loop, that seems to rise from the galaxy's disk at the upper right. Studied in the 1960s,...

Explanation: It looks like a double comet, but Comet PanSTARRS (C/2011 L4) is just offering skygazers a Messier moment. Outward bound and fading in this starry scene, the well-photographed comet is remarkably similar in brightness to M31, the Andromeda Galaxy. Tracking through northern skies just below the galaxy, the comet was captured as local midnight approached on April 3. Both comet and galaxy were visible to the eye and are immersed in the faint glow of northern lights as our own Milky Way galaxy arcs over a snowy field near Tänndalen, Sweden. Double star cluster h and chi Persei can...

Explanation: This beautiful, bright, spiral galaxy is Messier 64, often called the Black Eye Galaxy or the Sleeping Beauty Galaxy for its heavy-lidded appearance in telescopic views. M64 is about 17 million light-years distant in the otherwise well-groomed northern constellation Coma Berenices. In fact, the Red Eye Galaxy might also be an appropriate moniker in this colorful composition of narrow and wideband images. The enormous dust clouds obscuring the near-side of M64's central region are laced with the telltale reddish glow of hydrogen associated with star forming regions. But they are not this galaxy's only peculiar feature. Observations show that...

Explanation: The Great Nebula in Orion, an immense, nearby starbirth region, is probably the most famous of all astronomical nebulas. Here, glowing gas surrounds hot young stars at the edge of an immense interstellar molecular cloud only 1500 light-years away. In the above deep image in assigned colors highlighted by emission in oxygen and hydrogen, wisps and sheets of dust and gas are particularly evident. The Great Nebula in Orion can be found with the unaided eye near the easily identifiable belt of three stars in the popular constellation Orion. In addition to housing a bright open cluster of stars...

Explanation: The Whirlpool Galaxy is a classic spiral galaxy. At only 30 million light years distant and fully 60 thousand light years across, M51, also known as NGC 5194, is one of the brightest and most picturesque galaxies on the sky. The above image is a digital combination of a ground-based image from the 0.9-meter telescope at Kitt Peak National Observatory and a space-based image from the Hubble Space Telescope highlighting sharp features normally too red to be seen. Anyone with a good pair of binoculars, however, can see this Whirlpool toward the constellation of the Hunting Dogs (Canes Venatici....

Explanation: This infrared view from the Herschel Space Observatory explores the Andromeda Galaxy, the closest large spiral galaxy to our own Milky Way. Only 2.5 million light-years distant, the famous island universe is also known to astronomers as M31. Andromeda spans over 200,000 light-years making it more the twice the size of the Milky Way. Shown in false color, the image data reveal the cool dust lanes and clouds that still shine in the infrared but are otherwise dark and opaque at visual wavelengths. Red hues near the galaxy's outskirts represent the glow of dust heated by starlight to a...

Explanation: Barred spiral galaxy NGC 1365 is truly a majestic island universe some 200,000 light-years across. Located a mere 60 million light-years away toward the chemical constellation Fornax, NGC 1365 is a dominant member of the well-studied Fornax galaxy cluster. This sharp color image shows intense star forming regions at the ends of the bar and along the spiral arms, and details of dust lanes cutting across the galaxy's bright core. At the core lies a supermassive black hole. Astronomers think NGC 1365's prominent bar plays a crucial role in the galaxy's evolution, drawing gas and dust into a star-forming...

Explanation: A planetary nebula with a simple symmetry familiar to telescopic sky gazers, the Ring Nebula (M57) is some 2,000 light-years away in the musical constellation Lyra. Hints of changing colors and subtle details are brought out in this remarkable sketch of the cosmic ring. The sketch was made with 800x magnification and excellent seeing conditions directly at the eyepiece of a 40 inch reflecting telescope. Colored pencils on white paper were used to create the original drawing, shown here digitally scanned with an inverted palette applied. About one light-year across, the nebula is composed of outer layers expelled from...

Explanation: Giant elliptical galaxy M60 and spiral galaxy NGC 4647 do look like an odd couple in this sharp cosmic portrait from the Hubble Space Telescope. But they are found in a region of space where galaxies tend to gather, on the eastern side of the nearby Virgo Galaxy Cluster. About 54 million light-years distant, bright M60's simpler egg-like shape is created by its randomly swarming older stars, while NGC 4647's young blue stars, gas and dust are organized into winding arms rotating in a flattened disk. Spiral NGC 4647 is estimated to be more distant than M60, some 63...

Explanation: It was one of the most famous images of the 1990s. This image, taken with the Hubble Space Telescope in 1995, shows evaporating gaseous globules (EGGs) emerging from pillars of molecular hydrogen gas and dust. The giant pillars are light years in length and are so dense that interior gas contracts gravitationally to form stars. At each pillars' end, the intense radiation of bright young stars causes low density material to boil away, leaving stellar nurseries of dense EGGs exposed. The Eagle Nebula, associated with the open star cluster M16, lies about 7000 light years away. The pillars of...

Explanation: One of the last entries in Charles Messier's famous catalog, big, beautiful spiral galaxy M101 is definitely not one of the least. About 170,000 light-years across, this galaxy is enormous, almost twice the size of our own Milky Way Galaxy. M101 was also one of the original spiral nebulae observed with Lord Rosse's large 19th century telescope, the Leviathan of Parsontown. In contrast, this mulitwavelength view of the large island universe is a composite of images recorded by space-based telescopes in the 21st century. Color coded From X-rays to infrared wavelengths (high to low energies), the image data was...

Explanation: In 1716, English astronomer Edmond Halley noted, "This is but a little Patch, but it shews itself to the naked Eye, when the Sky is serene and the Moon absent." Of course, M13 is now modestly recognized as the Great Globular Cluster in Hercules, one of the brightest globular star clusters in the northern sky. Telescopic views reveal the spectacular cluster's hundreds of thousands of stars. At a distance of 25,000 light-years, the cluster stars crowd into a region 150 light-years in diameter, but approaching the cluster core upwards of 100 stars could be contained in a cube just...

Explanation: Follow the handle of the Big Dipper away from the dipper's bowl until you get to the handle's last bright star. Then, just slide your telescope a little south and west and you might find this stunning pair of interacting galaxies, the 51st entry in Charles Messier famous catalog. Perhaps the original spiral nebula, the large galaxy with well defined spiral structure is also cataloged as NGC 5194. Its spiral arms and dust lanes clearly sweep in front of its companion galaxy (top), NGC 5195. The pair are about 31 million light-years distant and officially lie within the angular...

Astronomy Picture of the Day 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. 2002 July 10 M51: Cosmic Whirlpool Credit & Copyright: Tony and Daphne Hallas Explanation: Follow the handle of the Big Dipper away from the dipper's bowl, until you get to the handle's last bright star. Then, just slide your telescope a little south and west and you'll likely find this stunning pair of interacting galaxies, the 51st entry in Charles Messier's famous catalog. Perhaps the original spiral nebula,...