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Explanation: South of Antares, in the tail of the nebula-rich constellation Scorpius, lies emission nebula IC 4628. Nearby hot, massive stars, millions of years young, radiate the nebula with invisible ultraviolet light, stripping electrons from atoms. The electrons eventually recombine with the atoms to produce the visible nebular glow, dominated by the red emission of hydrogen. At an estimated distance of 6,000 light-years, the region shown is about 250 light-years across, spanning an area equivalent to four full moons on the sky. The nebula is also cataloged as Gum 56 for Australian astronomer Colin Stanley Gum, but seafood-loving astronomers might...

Explanation: Three thousand light-years away, a dying star throws off shells of glowing gas. This image from the Hubble Space Telescope reveals the Cat's Eye Nebula to be one of the most complex planetary nebulae known. In fact, the features seen in the Cat's Eye are so complex that astronomers suspect the bright central object may actually be a binary star system. The term planetary nebula, used to describe this general class of objects, is misleading. Although these objects may appear round and planet-like in small telescopes, high resolution images reveal them to be stars surrounded by cocoons of gas...

Explanation: A camera fixed low to a tripod on a northern summer's eve captured the series of images used in this serene, southern Ontario skyscape. The lakeside view frames our fair galaxy above calm water and the night's quintessential luminous apparitions. But the trails of light are neither satellite glint, nor meteor flash, nor auroral glow. In the wide-field composite constructed with four consecutive 15 second exposures, a pulsing firefly enters at the right, first wandering toward the camera, then left and back toward the lake, the central Milky Way rising in the background.

Explanation: Approaching over the north pole after nearly a five-year journey, Juno enjoys a perspective on Jupiter not often seen, even by spacecraft from Earth that usually swing by closer to Jupiter's equator. Looking down toward the ruling gas giant from a distance of 10.9 million kilometers, the spacecraft's JunoCam captured this image with Jupiter's nightside and orbiting entourage of four large Galilean moons on June 21. JunoCam is intended to provide close-up views of the gas giant's cloudy zoned and belted atmosphere. On July 4 (July 5 UT) Juno is set to burn its main engine to slow down...

Explanation: How far are you from a naturally dark night sky? In increasing steps, this world map (medium | large) shows the effect of artificial night sky brightness on the visual appearance of the night sky. The brightness was modeled using high resolution satellite data and fit to thousands of night sky brightness measurements in recent work. Color-coded levels are compared to the natural sky brightness level for your location. For example, artificial sky brightness levels in yellow alter the natural appearance of the night sky. In red they hide the Milky Way in an artificial luminous fog. The results...

Explanation: This beautiful telephoto composition spans light-years in a natural night skyscape from the island of Crete. Looking south, exposures both track the stars and record a fixed foreground in three merged panels that cover a 10x12 degree wide field of view. The May 15 waxing gibbous moonlight illuminates the church and mountainous terrain. A mere 18 thousand light-years away, huge globular star cluster Omega Centauri (NGC 5139) shining above gives a good visual impression of its appearance in binoculars on that starry night. Active galaxy Centaurus A (NGC 5128) is near the top of the frame, some 11 million...

Explanation: What will NASA's Juno spacecraft find when it reaches Jupiter next Monday? Very little, if Juno does not survive Jupiter Orbit Insertion, a complex series of operations in an unknown environment just above Jupiter's cloud tops. If successful, as explained in the featured video, Juno will swoop around Jupiter, passing closer than any previous spacecraft. The goal is to decelerate, enter into a highly elliptical orbit, and begin two years of science operations. Juno's science mission objectives include mapping Jupiter's deep structure, determining how much water is in Jupiter's atmosphere, and exploring Jupiter's powerful magnetic field and how it...

Explanation: What's happening over the horizon? Although the scene may appear somehow supernatural, nothing more unusual is occurring than a setting Sun and some well placed clouds. Pictured above are anticrepuscular rays. To understand them, start by picturing common crepuscular rays that are seen any time that sunlight pours though scattered clouds. Now although sunlight indeed travels along straight lines, the projections of these lines onto the spherical sky are great circles. Therefore, the crepuscular rays from a setting (or rising) sun will appear to re-converge on the other side of the sky. At the anti-solar point 180 degrees around...

Explanation: The New Horizons spacecraft took some stunning images of Jupiter on its way out to Pluto. Famous for its Great Red Spot, Jupiter is also known for its regular, equatorial cloud bands, visible through even modest sized telescopes. The featured image, horizontally compressed, was taken in 2007 near Jupiter's terminator and shows the Jovian giant's wide diversity of cloud patterns. On the far left are clouds closest to Jupiter's South Pole. Here turbulent whirlpools and swirls are seen in a dark region, dubbed a belt, that rings the planet. Even light colored regions, called zones, show tremendous structure, complete...

Explanation: Near the horizon the Full Moon often seems to loom large, swollen in appearance by the famous Moon illusion. But timelapse images demonstrate that the Moon's apparent size doesn't really change as it climbs toward the zenith. Its color does, though. Recording a frame every 10 seconds, this image shows how dramatic that color change can be. The composite follows a solstice Full Moon climbing above a rugged horizon over northwestern Indiana. A shrinking line-of-sight through planet Earth's dense and dusty atmosphere shifted the moonlight from strawberry red through honey-colored and paler yellowish hues. That change seems appropriate for...

Explanation: These three bright nebulae are often featured in 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 left of center, and colorful M20 near the bottom of the frame The third, NGC 6559, is right of M8, separated from the larger nebula by dark dust lanes. All three are stellar nurseries about five thousand light-years or so distant. The expansive M8, over a hundred light-years across, is also known as the Lagoon Nebula. M20's popular moniker is...

Explanation: A Full Moon sets as the Solstice Sun rises in this June 20 dawn skyscape. Captured from a nearby peak in central California, planet Earth, the scene looks across the summit of Mount Hamilton and Lick Observatory domes on a calendar date that marks an astronomical change of seasons and hemispherical extremes of daylight hours. Earth's shadow stretches toward the Santa Cruz Mountains on the western horizon. Just above the atmospheric grey shadowband is a more colorful anti-twilight arch, a band of reddened, backscattered sunlight also known as the Belt of Venus. The interplay of solstice dates and lunar...

Explanation: What's that over Paris? Cirrus. Typically, cirrus clouds appear white or gray when reflecting sunlight, can appear dark at sunset (or sunrise) against a better lit sky. Cirrus are among the highest types of clouds and are usually thin enough to see stars through. Cirrus clouds may form from moisture released above storm clouds and so may herald the arrival of a significant change in weather. Conversely, cirrus clouds have also been seen on Mars, Jupiter, Saturn, Titan, Uranus, and Neptune. The featured image was taken two days ago from a window in District 15, Paris, France, Earth. The...

Explanation: In the center of this serene stellar swirl is likely a harrowing black-hole beast. The surrounding swirl sweeps around billions of stars which are highlighted by the brightest and bluest. The breadth and beauty of the display give the swirl the designation of a grand design spiral galaxy. The central beast shows evidence that it is a supermassive black hole about 10 million times the mass of our Sun. This ferocious creature devours stars and gas and is surrounded by a spinning moat of hot plasma that emits blasts of X-rays. The central violent activity gives it the designation...

Explanation: Today the Sun reaches its northernmost point in planet Earth's sky. Called a solstice, the date traditionally marks a change of seasons -- from spring to summer in Earth's Northern Hemisphere and from fall to winter in Earth's Southern Hemisphere. The featured image was taken during the week of the 2008 summer solstice at Stonehenge in United Kingdom, and captures a picturesque sunrise involving fog, trees, clouds, stones placed about 4,500 years ago, and a 4.5 billion year old large glowing orb. Even given the precession of the Earth's rotational axis over the millennia, the Sun continues to rise...

Explanation: What's older than these ancient trees? Nobody you know -- but almost everything in the background of this picture. The trees are impressively old -- each part of the Ancient Bristlecone Pine Forest located in eastern California, USA. There, many of the oldest trees known are located, some dating as far back as about 5,000 years. Seemingly attached to tree branches, but actually much farther in the distance, are the bright orbs of Saturn (left) and Mars. These planets formed along with the Earth and the early Solar System much earlier -- about 4.5 billion years ago. Swooping down...

Explanation: Pluto's pitted plains meet rugged highlands in this stunning view. On the left lies a southeastern extent of the bright region still informally known as Sputnik Planum. At right the edge of a dark region, informally Krun Macula, rises some 2.5 kilometers above the icy plains. Along the boundary, connected clusters of large pits form deep valleys, some over 40 kilometers long with shadowy floors. Nitrogen ice is likely responsible for the more reflective plains. The dark red color of the highlands is thought to be from complex compounds called tholins, a product of ultraviolet light induced chemical reactions...

Explanation: Now approaching our fair planet this Comet PanSTARRS (C/2013 X1) will come closest on June 21-22, a mere 5.3 light-minutes away. By then its appearance low in northern hemisphere predawn skies (high in the south), will be affected by the light of a nearly Full Moon, though. Still the comet's pretty green coma is about the apparent size of the Full Moon in this telescopic portrait, captured on June 12 from the southern hemisphere's Siding Spring Observatory. The deep image also follows a broad, whitish dust tail up and toward the left in the frame, sweeping away from the...

Explanation: The Aurora Borealis or northern lights are familiar visitors to night skies above the village of Reine in the Lofoten Islands, Norway, planet Earth. In this scene, captured from a mountaintop camp site, the auroral curtains do seem to create an eerie tension with the coastal lights though. A modern perspective on the world at night, the stunning image was chosen as the over all winner in The World at Night's 2016 International Earth and Sky Photo Contest. Selections were made from over 900 entries highlighting the beauty of the night sky and its battle with light pollution.

Explanation: A new sky is becoming visible. When you look up, you see the sky as it appears in light -- electromagnetic radiation. But just over the past year, humanity has begun to see our once-familiar sky as it appears in a different type of radiation -- gravitational radiation. Today, the LIGO collaboration is reporting the detection of GW151226, the second confirmed flash of gravitational radiation after GW150914, the historic first detection registered three months earlier. As its name implies, GW151226 was recorded in late December of 2015. It was detected simultaneously by both LIGO facilities in Washington and Louisiana,...