Posing near the western horizon, a brilliant evening star and slender young crescent shared reflections in a calm sea last Thursday after sunset. Recorded in this snapshot from the Atlantic beach at Santa Marinella near Rome, Italy, the lovely celestial conjunction of the two brightest beacons in the night sky could be enjoyed around the world. Seaside, light reflected by briefly horizontal surfaces of the gentle waves forms the shimmering columns across the water. Similar reflections by fluttering atmospheric ice crystals can create sometimes mysterious pillars of light. Of course, earthlight itself visibly illuminates the faint lunar night side.
Captured last week after sunset on a Chilean autumn night, an exceptional airglow floods this allsky view from Las Campanas Observatory. The airglow was so intense it diminished parts of the Milky Way as it arced horizon to horizon above the high Atacama desert. Originating at an altitude similar to aurorae, the luminous airglow is due to chemiluminescence, the production of light through chemical excitation. Commonly recorded in color by sensitive digital cameras, the airglow emission here is fiery in appearance. It is predominately from atmospheric oxygen atoms at extremely low densities and has often been present during southern hemisphere nights over the last few years. Like the Milky Way, on that dark night the strong airglow was very visible to the eye, but seen without color. Jupiter is brightest celestial beacon though, standing opposite the Sun and near the central bulge of the Milky Way rising above the eastern (top) horizon. The Large and Small Magellanic clouds both shine through the airglow to the lower left of the galactic plane, toward the southern horizon.
This image is not blurry. It shows in clear detail that the largest satellite galaxy to our Milky Way, the Large Cloud of Magellan (LMC), rotates. First determined with Hubble, the rotation of the LMC is presented here with fine data from the Sun-orbiting Gaia satellite. Gaia measures the positions of stars so accurately that subsequent measurements can reveal slight proper motions of stars not previously detectable. The featured image shows, effectively, exaggerated star trails for millions of faint LMC stars. Inspection of the image also shows the center of the clockwise rotation: near the top of the LMC’s central bar. The LMC, prominent in southern skies, is a small spiral galaxy that has been distorted by encounters with the greater Milky Way Galaxy and the lesser Small Magellanic Cloud (SMC).
What lies at the bottom of Hyperion‘s strange craters? To help find out, the robot Cassini spacecraft now orbiting Saturn swooped past the sponge-textured moon in 2005 and 2010 and took images of unprecedented detail. A six-image mosaic from the 2005 pass, featured here in natural color, shows a remarkable world strewn with strange craters and an odd sponge-like surface. At the bottom of most craters lies some type of unknown dark reddish material. This material appears similar to that covering part of another of Saturn’s moons, Iapetus, and might sink into the ice moon as it better absorbs warming sunlight. Hyperion is about 250 kilometers across, rotates chaotically, and has a density so low that it likely houses a vast system of caverns inside.
Why does a volcanic eruption sometimes create lightning? Pictured above, the Sakurajima volcano in southern Japan was caught erupting in 2013 January. Magma bubbles so hot they glowed shot away as liquid rock burst through the Earth’s surface from below. The featured image is particularly notable, however, for the lightning bolts caught near the volcano’s summit. Why lightning occurs even in common thunderstorms remains a topic of research, and the cause of volcanic lightning is even less clear. Surely, lightning bolts help quench areas of opposite but separated electric charges. Volcanic lightning episodes may be facilitated by charge-inducing collisions in volcanic dust. Lightning is usually occurring somewhere on Earth, typically over 40 times each second.
A recent informal poll found that astronomers don’t yet have a good collective noun for a group of black holes, but they need one. The red circles in this Chandra Observatory X-ray image identify a group of a dozen black holes that are members of binary star systems. With 5 to 30 times the mass of the Sun, the black hole binaries are swarming within about 3 light-years of the center of our galaxy where the supermassive black hole identified as Sagittarius A* (Sgr A*) resides. Yellow circles indicate X-ray sources that are likely less massive neutron stars or white dwarf stars in binary star systems. Alone, black holes would be invisible, but as part of a binary star system they accrete material from their normal companion star and generate X-rays. At the distance of the galactic center Chandra can detect only the brighter of these black hole binary systems as point-like sources of X-rays, hinting that many fainter X-ray emitting black hole binaries should exist there, as yet undetected.
How was the unusual Red Rectangle nebula created? At the nebula’s center is an aging binary star system that surely powers the nebula but does not, as yet, explain its colors. The unusual shape of the Red Rectangle is likely due to a thick dust torus which pinches the otherwise spherical outflow into tip-touching cone shapes. Because we view the torus edge-on, the boundary edges of the cone shapes seem to form an X. The distinct rungs suggest the outflow occurs in fits and starts. The unusual colors of the nebula are less well understood, however, and speculation holds that they are partly provided by hydrocarbon molecules that may actually be building blocks for organic life. The Red Rectangle nebula lies about 2,300 light years away towards the constellation of the Unicorn (Monoceros). The nebula is shown here in great detail as recently reprocessed image from Hubble Space Telescope. In a few million years, as one of the central stars becomes further depleted of nuclear fuel, the Red Rectangle nebula will likely bloom into a planetary nebula.
How far can you see? Everything you can see, and everything you could possibly see, right now, assuming your eyes could detect all types of radiations around you — is the observable universe. In visible light, the farthest we can see comes from the cosmic microwave background, a time 13.8 billion years ago when the universe was opaque like thick fog. Some neutrinos and gravitational waves that surround us come from even farther out, but humanity does not yet have the technology to detect them. The featured image illustrates the observable universe on an increasingly compact scale, with the Earth and Sun at the center surrounded by our Solar System, nearby stars, nearby galaxies, distant galaxies, filaments of early matter, and the cosmic microwave background. Cosmologists typically assume that our observable universe is just the nearby part of a greater entity known as “the universe” where the same physics applies. However, there are several lines of popular but speculative reasoning that assert that even our universe is part of a greater multiverse where either different physical constants occur, different physical laws apply, higher dimensions operate, or slightly different-by-chance versions of our standard universe exist.
Why is there a large boulder near the center of Tycho’s peak? Tycho crater on the Moon is one of the easiest features to see, visible even to the unaided eye (inset, lower right). But at the center of Tycho (inset, upper left) is a something unusual — a 120-meter boulder. This boulder was imaged at very high resolution at sunrise, over the past decade, by the Moon-circling Lunar Reconnaissance Orbiter (LRO). The leading origin hypothesis is that that the boulder was thrown during the tremendous collision that formed Tycho crater about 110 million years ago, and by chance came back down right near the center of the newly-formed central mountain. Over the next billion years meteor impacts and moonquakes should slowly degrade Tycho‘s center, likely causing the central boulder to tumble 2000 meters down to the crater floor and disintegrate.
Sometimes land and sky are both busy and beautiful. The landscape pictured in the foreground encompasses Bryce Canyon in Utah, USA, famous for its many interesting rock structures eroded over millions of years. The featured skyscape, photogenic in its own right, encompasses the arching central disk of our Milky Way Galaxy, the short streaks of three passing planes near the horizon, at least four long streaks that are likely Eta Aquariid meteors, and many stars including the three bright stars that make up the Summer Triangle. The featured image is a digital panorama created from 12 smaller images during this date in 2014. Recurring every year, yesterday and tonight mark the peak of this year’s Eta Aquriids meteor shower, where a patient observer with dark skies and dark-adapted eyes might expect to see a meteor every few minutes.