Spiral Galaxy NGC 6744


Beautiful spiral galaxy NGC 6744 is nearly 175,000 light-years across, larger than our own Milky Way. It lies some 30 million light-years distant in the southern constellation Pavo and appears as only a faint, extended object in small telescopes. We see the disk of the nearby island universe tilted towards our line of sight in this remarkably detailed galaxy portrait, a telescopic view that spans an area about the angular size of a full moon. In it, the giant galaxy’s elongated yellowish core is dominated by the light from old, cool stars. Beyond the core, grand spiral arms are filled with young blue star clusters and speckled with pinkish star forming regions. An extended arm sweeps past a smaller satellite galaxy (NGC 6744A) at the lower right. NGC 6744’s galactic companion is reminiscent of the Milky Way’s satellite galaxy the Large Magellanic Cloud.

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Electric Night


It may appear, at first, like the Galaxy is producing the lightning, but really it’s the Earth. The featured nighttime landscape was taken from a southern tip of the Italian Island of Sardinia in early June. The foreground rocks and shrubs are near the famous Capo Spartivento Lighthouse, and the camera is pointed south toward Algeria in Africa. In the distance, across the Mediterranean Sea, a thunderstorm is threatening, with several electric lightning strokes caught together during this 25-second wide-angle exposure. Much farther in the distance, strewn about the sky, are hundreds of stars in the neighborhood of our Sun in the Milky Way Galaxy. Furthest away, and slanting down from the upper left, are billions of stars that together compose the central band of our Milky Way.

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M27: The Dumbbell Nebula


Is this what will become of our Sun? Quite possibly. The first hint of our Sun‘s future was discovered inadvertently in 1764. At that time, Charles Messier was compiling a list of diffuse objects not to be confused with comets. The 27th object on Messier’s list, now known as M27 or the Dumbbell Nebula, is a planetary nebula, the type of nebula our Sun will produce when nuclear fusion stops in its core. M27 is one of the brightest planetary nebulae on the sky, and can be seen toward the constellation of the Fox (Vulpecula) with binoculars. It takes light about 1000 years to reach us from M27, featured here in colors emitted by hydrogen and oxygen. Understanding the physics and significance of M27 was well beyond 18th century science. Even today, many things remain mysterious about bipolar planetary nebula like M27, including the physical mechanism that expels a low-mass star’s gaseous outer-envelope, leaving an X-ray hot white dwarf.

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Mercury Crosses a Quiet Sun


What’s that black dot crossing the Sun? The planet Mercury. Mercury usually passes over or under the Sun, as seen from Earth, but last month the Solar System’s innermost planet appeared to go just about straight across the middle. Although witnessed by planet admirers across the globe, a particularly clear view was captured by the Solar Dynamics Observatory (SDO) in Earth orbit. The featured video was captured by the SDO’s HMI instrument in a broad range of visible light, and compresses the 5 1/2 hour transit into about 13 seconds. The background Sun was unusually quiet — even for being near Solar Minimum — and showed no sunspots. The next solar transit by Mercury will occur in 2032.

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Starburst Galaxy M94 from Hubble


Why does this galaxy have a ring of bright blue stars? Beautiful island universe Messier 94 lies a mere 15 million light-years distant in the northern constellation of the Hunting Dogs (Canes Venatici). A popular target for Earth-based astronomers, the face-on spiral galaxy is about 30,000 light-years across, with spiral arms sweeping through the outskirts of its broad disk. But this Hubble Space Telescope field of view spans about 7,000 light-years across M94‘s central region. The featured close-up highlights the galaxy’s compact, bright nucleus, prominent inner dust lanes, and the remarkable bluish ring of young massive stars. The ring stars are all likely less than 10 million years old, indicating that M94 is a starburst galaxy that is experiencing an epoch of rapid star formation. The circular ripple of blue stars is likely a wave propagating outward, having been triggered by the gravity and rotation of a oval matter distributions. Because M94 is relatively nearby, astronomers can better explore details of its starburst ring.

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Star Trails for a Red Planet


Does Mars have a north star? In long exposures of Earth’s night sky, star trails make concentric arcs around the north celestial pole, the direction of our fair planet’s axis of rotation. Bright star Polaris is presently the Earth’s North Star, close on the sky to Earth’s north celestial pole. But long exposures on Mars show star trails too, concentric arcs about a celestial pole determined by Mars’ axis of rotation. Tilted like planet Earth’s, the martian axis of rotation points in a different direction in space though. It points to a place on the sky between stars in Cygnus and Cepheus with no bright star comparable to Earth’s north star Polaris nearby. So even though this ruddy, weathered landscape is remarkably reminiscent of terrain in images from the martian surface, the view must be from planet Earth, with north star Polaris near the center of concentric star trails. The landforms in the foreground are found in Qinghai Province in northwestern China.

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Galileo s Europa Remastered


Looping through the Jovian system in the late 1990s, the Galileo spacecraft recorded stunning views of Europa and uncovered evidence that the moon’s icy surface likely hides a deep, global ocean. Galileo’s Europa image data has been remastered here, using improved new calibrations to produce a color image approximating what the human eye might see. Europa’s long curving fractures hint at the subsurface liquid water. The tidal flexing the large moon experiences in its elliptical orbit around Jupiter supplies the energy to keep the ocean liquid. But more tantalizing is the possibility that even in the absence of sunlight that process could also supply the energy to support life, making Europa one of the best places to look for life beyond Earth. What kind of life could thrive in a deep, dark, subsurface ocean? Consider planet Earth’s own extreme shrimp.

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