Separated by about 14 degrees (28 Full Moons) in planet Earth’s sky, spiral galaxies M31 at left, and M33 are both large members of the Local Group, along with our own Milky Way galaxy. This narrow- and wide-angle, multi-camera composite finds details of spiral structure in both, while the massive neighboring galaxies seem to be balanced in starry fields either side of bright Mirach, beta star in the constellation Andromeda. Mirach is just 200 light-years from the Sun. But M31, the Andromeda Galaxy, is really 2.5 million light-years distant and M33, the Triangulum Galaxy, is also about 3 million light years away. Although they look far apart, M31 and M33 are engaged in a gravitational struggle. In fact, radio astronomers have found indications of a bridge of neutral hydrogen gas that could connect the two, evidence of a closer encounter in the past. Based on measurements, gravitational simulations currently predict that the Milky Way, M31, and M33 will all undergo mutual close encounters and potentially mergers, billions of years in the future.

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A mountainous region informally known as Tartarus Dorsa sprawls some 530 kilometers (330 miles) across this Plutonian landscape. Recently downloaded from New Horizons, it combines blue, red, and infrared image data in an extended color view captured near the spacecraft’s close approach to Pluto on July 14. Shadows near the terminator, the line between Pluto’s dim day and night, emphasize a rough, scaly texture. The stunning image resolves details on the distant world about 1.3 kilometers (0.8 miles) across. Refering to a part of Hades in ancient Greek mythology, Tartarus Dorsa borders Tombaugh Regio to the east.

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Stars are forming in dark, dusty molecular cloud LDN 988. Seen near picture center some 2,000 light-years distant, LDN 988 and other nearby dark nebulae were cataloged by Beverly T. Lynds in 1962 using Palomar Observatory Sky Survey plates. Narrowband and near-infrared explorations of the dark nebula reveal energetic shocks and outflows light-years across associated with dozens of newborn stars. But in this sharp optical telescopic view, the irregular outlines of LDN 988 and friends look like dancing stick figures eclipsing the rich starfields of the constellation Cygnus. From dark sky sites the region can be identified by eye alone. It’s part of the Great Rift of dark nebulae along the plane of the Milky Way galaxy known as the Northern Coalsack.

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Does the Sun return to the same spot on the sky every day? No. A better and more visual answer to that question is an analemma, a composite image taken from the same spot at the same time over the course of a year. The featured weekly analemma was taken despite cold temperatures and high winds near the Concordia Station in Antarctica. The position of the Sun at 4 pm was captured on multiple days in the digital composite image, believed to be the first analemma constructed from Antarctica. The reason the image only shows the Sun from September to March is because the Sun was below the horizon for much of the rest of the year. In fact, today being an equinox, the Sun rises today at the South Pole after a six month absence and won’t set again until the next equinox in March, baring large atmospheric refraction effects. Conversely, today the Sun sets at the North Pole after half a year of continuous daylight. For all of the Earth in between, though, the equinox means that today will have a nighttime and daytime that are both 12 hours long.

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What are those streaks of light in the sky? First and foremost, the arching structure is the central band of our Milky Way galaxy. Visible in this galactic band are millions of distant stars mixed with numerous lanes of dark dust. Harder to discern is a nearly vertical beam of light rising from the horizon, just to the right of the image center. This beam is zodiacal light, sunlight scattered by dust in our Solar System that may be surprisingly prominent just after sunset or just before sunrise. In the foreground are several telescopes of the Bosque Alegre Astrophysical Station of the National University of Cordoba in Argentina. The station schedules weekend tours and conducts research into the nature of many astronomical objects including comets, active galaxies, and clusters of galaxies. The featured image was taken early this month.

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Dust lanes seem to swirl around the core of Messier 96 in this colorful, detailed portrait of the center of a beautiful island universe. Of course M96 is a spiral galaxy, and counting the faint arms extending beyond the brighter central region, it spans 100 thousand light-years or so, making it about the size of our own Milky Way. M96, also known as NGC 3368, is known to be about 35 million light-years distant and a dominant member of the Leo I galaxy group. The featured image was taken by the Hubble Space Telescope. The reason for M96‘s asymmetry is unclear — it could have arisen from gravitational interactions with other Leo I group galaxies, but the lack of an intra-group diffuse glow seems to indicate few recent interactions. Galaxies far in the background can be found by examining the edges of the picture.

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Do some surface features on Enceladus roll like a conveyor belt? A leading interpretation of images taken of Saturn’s most explosive moon indicate that they do. This form of asymmetric tectonic activity, very unusual on Earth, likely holds clues to the internal structure of Enceladus, which may contain subsurface seas where life might be able to develop. Pictured above is a composite of 28 images taken by the robotic Cassini spacecraft in 2008 just after swooping by the ice-spewing orb. Inspection of these images show clear tectonic displacements where large portions of the surface all appear to move all in one direction. On the image right appears one of the most prominent tectonic divides: Labtayt Sulci, a canyon about one kilometer deep. The small magnitude of Enceladus’ wobble as it orbits Saturn might indicate damping by a globally extending underground ocean layer.

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This eerie landscape of incandescent plasma suspended in looping and twisted magnetic fields stretched toward the Sun’s eastern horizon on September 16. Captured through a backyard telescope and narrowband filter in light from ionized hydrogen, the scene reveals a gigantic prominence lofted above the solar limb. Some 600,000 kilometers across, the magnetized plasma wall would dwarf worlds of the Solar System. Ruling gas giant Jupiter can only boast a diameter of 143,000 kilometers or so, while planet Earth’s diameter is less than 13,000 kilometers. Known as a hedgerow prominence for its appearance, the enormous structure is far from stable though, and such large solar prominences often erupt.

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This shadowy landscape of majestic mountains and icy plains stretches toward the horizon of a small, distant world. It was captured from a range of about 18,000 kilometers when New Horizons looked back toward Pluto, 15 minutes after the spacecraft’s closest approach on July 14. The dramatic, low-angle, near-twilight scene follows rugged mountains still popularly known as Norgay Montes from foreground left, and Hillary Montes along the horizon, giving way to smooth Sputnik Planum at right. Layers of Pluto’s tenuous atmosphere are also revealed in the backlit view. With a strangely familiar appearance, the frigid terrain likely includes ices of nitrogen and carbon monoxide with water-ice mountains rising up to 3,500 meters (11,000 feet). That’s comparable in height to the majestic mountains of planet Earth. This Plutonian landscape is 380 kilometers (230 miles) across.

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Chaotic in appearance, these filaments of shocked, glowing gas break across planet Earth’s sky toward the constellation of Cygnus, as part of the Veil Nebula. The Veil Nebula itself 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. Blasted out in the cataclysmic event, the interstellar shock waves plow through space sweeping up and exciting interstellar material. The glowing filaments are really more like long ripples in a sheet seen almost edge on, remarkably well separated into the glow of ionized hydrogen and sulfur atoms shown in red and green, and oxygen in blue hues. Also known as the Cygnus Loop, the Veil Nebula now spans nearly 3 degrees or about 6 times the diameter of the full Moon. While that translates to over 70 light-years at its estimated distance of 1,500 light-years, this field of view spans less than one third that distance. Identified as Pickering’s Triangle for a director of Harvard College Observatory and cataloged as NGC 6979, the complex of filaments might be more appropriately known as Williamina Fleming’s Triangular Wisp.

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