Why would you want to fake a universe? For one reason — to better understand our real universe. Many astronomical projects seeking to learn properties of our universe now start with a robotic telescope taking sequential images of the night sky. Next, sophisticated computer algorithms crunch these digital images to find stars and galaxies and measure their properties. To calibrate these algorithms, it is useful to test them on fake images from a fake universe to see if the algorithms can correctly deduce purposely imprinted properties. The featured mosaic of fake images was created to specifically mimic the images that have appeared on NASA’s Astronomy Picture of the Day (APOD). Only one image of the 225 images is real — can you find it? The accomplished deceptors have made available individual fake APOD images that can be displayed by accessing their ThisIsNotAnAPOD webpage or Twitter feed. More useful for calibrating and understanding our distant universe, however, are fake galaxies — a sampling of which can be seen at their ThisIsNotAGalaxy webpage. via NASA https://ift.tt/3BXJs1E

Why, sometimes, does part of the Sun’s atmosphere leap into space? The reason lies in changing magnetic fields that thread through the Sun’s surface. Regions of strong surface magnetism, known as active regions, are usually marked by dark sunspots. Active regions can channel charged gas along arching or sweeping magnetic fields — gas that sometimes falls back, sometimes escapes, and sometimes not only escapes but impacts our Earth. The featured one-hour time-lapse video — taken with a small telescope in France — captured an eruptive filament that appeared to leap off the Sun late last month. The filament is huge: for comparison, the size of the Earth is shown on the upper left. Just after the filament lifted off, the Sun emitted a powerful X-class flare while the surface rumbled with a tremendous solar tsunami. A result was a cloud of charged particles that rushed into our Solar System but mostly missed our Earth — this time. However, enough solar plasma did impact our Earth’s magnetosphere to create a few faint auroras. via NASA https://ift.tt/3odF9dU

To some it looks like a cat’s eye. To others, perhaps like a giant cosmic conch shell. It is actually one of brightest and most highly detailed planetary nebula known, composed of gas expelled in the brief yet glorious phase near the end of life of a Sun-like star. This nebula’s dying central star may have produced the outer circular concentric shells by shrugging off outer layers in a series of regular convulsions. The formation of the beautiful, complex-yet-symmetric inner structures, however, is not well understood. The featured image is a composite of a digitally sharpened Hubble Space Telescope image with X-ray light captured by the orbiting Chandra Observatory. The exquisite floating space statue spans over half a light-year across. Of course, gazing into this Cat’s Eye, humanity may well be seeing the fate of our sun, destined to enter its own planetary nebula phase of evolution … in about 5 billion years. via NASA https://ift.tt/3GUtbOG

On an August night two friends enjoyed this view after a day’s hike on the Plateau d’Emparis in the French Alps. At 2400 meters altitude the sky was clear. Light from a setting moon illuminates the foreground captured in the simple vertical panorama of images. Along the plane of our Milky Way galaxy stars of Cassiopeia and Perseus shine along the panorama’s left edge. But seen as a faint cloud with a brighter core, the Andromeda galaxy, stands directly above the two friends in the night. The nearest large spiral galaxy, Andromeda is about 2.5 million light-years beyond the stars of the Milky Way. Adding to the evening’s shared extragalactic perspective, the fainter fuzzy spot in the sky right between them is M33, also known as the Triangulum galaxy. Third largest in the local galaxy group, after Andromeda and Milky Way, the Triangulum galaxy is about 3 million light-years distant. On that night, the two friends stood about 3 light-nanoseconds apart. via NASA https://ift.tt/3o37inF

Light-years across, this suggestive shape known as the Seahorse Nebula appears in silhouette against a rich, luminous background of stars. Seen toward the royal northern constellation of Cepheus, the dusty, obscuring clouds are part of a Milky Way molecular cloud some 1,200 light-years distant. It is also listed as Barnard 150 (B150), one of 182 dark markings of the sky cataloged in the early 20th century by astronomer E. E. Barnard. Packs of low mass stars are forming within, but their collapsing cores are only visible at long infrared wavelengths. Still, the colorful stars of Cepheus add to this pretty, galactic skyscape. via NASA https://ift.tt/3o5NRuG

Dwarf galaxies NGC 147 (left) and NGC 185 stand side by side in this sharp telescopic portrait. The two are not-often-imaged satellites of M31, the great spiral Andromeda Galaxy, some 2.5 million light-years away. Their separation on the sky, less than one degree across a pretty field of view, translates to only about 35 thousand light-years at Andromeda’s distance, but Andromeda itself is found well outside this frame. Brighter and more famous satellite galaxies of Andromeda, M32 and M110, are seen closer to the great spiral. NGC 147 and NGC 185 have been identified as binary galaxies, forming a gravitationally stable binary system. But recently discovered faint dwarf galaxy Cassiopeia II also seems to be part of their system, forming a gravitationally bound group within Andromeda’s intriguing population of small satellite galaxies. via NASA https://ift.tt/3q5uhkA

The Horsehead Nebula is one of the most famous nebulae on the sky. It is visible as the dark indentation to the orange emission nebula at the far right of the featured picture. The horse-head feature is dark because it is really an opaque dust cloud that lies in front of the bright emission nebula. Like clouds in Earth’s atmosphere, this cosmic cloud has assumed a recognizable shape by chance. After many thousands of years, the internal motions of the cloud will surely alter its appearance. The emission nebula’s orange color is caused by electrons recombining with protons to form hydrogen atoms. Toward the lower left of the image is the Flame Nebula, an orange-tinged nebula that also contains intricate filaments of dark dust. Two prominent reflection nebulas are visible: round IC 432 on the far left, and blue NGC 2023 just to the lower left of the Horsehead nebula. Each glows primarily by reflecting the light of their central star. via NASA https://ift.tt/3q5loYi

We’ve seen this same supernova three times — when will we see it a fourth? When a distant star explodes in a supernova, we’re lucky if we see it even once. In the case of AT 2016jka (« SN Requiem »), because the exploding star happened to be lined up behind the center of a galaxy cluster (MACS J0138 in this case), a comparison of Hubble Space Telescope images demonstrate that we saw it three times. These three supernova images are highlighted in circles near the bottom of the left frame taken in 2016. On the right frame, taken in 2019, the circles are empty because all three images of the single supernova had faded. Computer modeling of the cluster lens, however, indicates that a fourth image of the same supernova should eventually appear in the upper circle on the right image. But when? The best models predict this will happen in 2037, but this date is uncertain by about two years because of ambiguities in the mass distribution of the cluster lens and the brightness history of the stellar explosion. With refined predictions and vigilant monitoring, Earthlings living 16 years from now may be able to catch this fourth image — and perhaps learn more about both galaxy clusters and supernovas at once. via NASA https://ift.tt/3CD5CaC

The dream was to capture both the waterfall and the Milky Way together. Difficulties included finding a good camera location, artificially illuminating the waterfall and the surrounding valley effectively, capturing the entire scene with numerous foreground and background shots, worrying that fireflies would be too distracting, keeping the camera dry, and avoiding stepping on a poisonous snake. Behold the result — captured after midnight in mid-July and digitally stitched into a wide-angle panorama. The waterfall is the picturesque Zhulian waterfall in the Luoxiao Mountains in eastern Hunan Province, China. The central band of our Milky Way Galaxy crosses the sky and shows numerous dark dust filaments and colorful nebulas. Bright stars dot the sky — all residing in the nearby Milky Way — including the Summer Triangle with bright Vega visible above the Milky Way’s arch. After capturing all 78 component exposures for you to enjoy, the photographer and friends enjoyed the view themselves for the rest of the night. via NASA https://ift.tt/3mvKkpC

Is our universe haunted? It might look that way on this dark matter map. The gravity of unseen dark matter is the leading explanation for why galaxies rotate so fast, why galaxies orbit clusters so fast, why gravitational lenses so strongly deflect light, and why visible matter is distributed as it is both in the local universe and on the cosmic microwave background. The featured image from the American Museum of Natural History’s Hayden Planetarium Space Show Dark Universe highlights one example of how pervasive dark matter might haunt our universe. In this frame from a detailed computer simulation, complex filaments of dark matter, shown in black, are strewn about the universe like spider webs, while the relatively rare clumps of familiar baryonic matter are colored orange. These simulations are good statistical matches to astronomical observations. In what is perhaps a scarier turn of events, dark matter — although quite strange and in an unknown form — is no longer thought to be the strangest source of gravity in the universe. That honor now falls to dark energy, a more uniform source of repulsive gravity that seems to now dominate the expansion of the entire universe. via NASA https://ift.tt/2ZNKLmF