These glowing wisps are the visible remains of a star that went supernova about 7,000 years ago. Today the supernova remnant is known as the Veil Nebula and is visible only through telescopes. In the image, red marks hydrogen gas and blue marks oxygen. First carried by shock waves, these remains of a former star now serve as seed material for other stars and planetary systems to form. (Image credit: A. Alharbi; via APOD)
Category: Phenomena
Understanding Acoustic Dissonance
Dissonance — the discomfort we feel when two or more musical notes feel mismatched — is more than just a subjective measure. In this video, Henry of Minute Physics delves into some of the physics involved in dissonance, first with simple sine waves and then with musical instruments. Our ears — and our brains — seem most troubled when two notes (and their overtones) are close but not quite matching in frequency. And, as Henry explains, the peaks and valleys between those agreements lead to many of the musical systems we have today. (Video and image credit: Minute Physics)
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Cutting Out Canyons
Over the millennia, the Colorado River has carved some of the deepest and most dramatic canyons on our planet. This astronaut photo shows the river near its dam at Lake Powell. The strip of white edging the lake is the “bathtub ring” that shows how the water level has varied over the years. The deep canyons — over 400 meters from the Horn in the center of the photo to the river beside it — throw shadows across the landscape. To reach these depths, the Colorado River incised its path into bedrock that was tectonically uplifted. (Image credit: NASA; via NASA Earth Observatory)
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Crown Splash
When a falling drop hits a thin layer of water, the impact sends up a thin, crown-shaped splash. This research poster shows a numerical simulation of such a splash in the throes of various instabilities. The crown’s thick edges are undergoing a Rayleigh-Plateau instability, breaking into droplets much the way a dripping faucet does. On the far side, the crown has rapidly expanding holes that pull back and collide. The still-intact liquid sheet at the base of the crown shows some waviness, as well, hinting at a growing instability there. (Image credit: L. Kahouadji et al.)
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A Sprite From Orbit
A sprite, also known as a red sprite, is an upper-atmospheric electrical discharge sometimes seen from thunderstorms. Unlike lightning, sprites discharge upward from the storm toward the ionosphere. This particular one was captured by an astronaut aboard the International Space Station. That’s a pretty incredible feat because sprites typically only last a millisecond or so. The first one wasn’t photographed until 1989. (Image credit: NASA; via P. Byrne)
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A Variety of Vortices
Winds parted around the Kuril Islands and left behind a string of vortices in this satellite image from April 2025. This pattern of alternating vortices is known as a von Karman vortex street. The varying directions of the vortex streets show that winds across the islands ranged from southeasterly to southerly. Notice also that the size of the island dictates the size of the vortices. Larger islands create larger vortices, and smaller islands have smaller and more frequent vortices. (Image credit: M. Garrison; via NASA Earth Observatory)
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Dancing Metal Droplets
Droplets of a gallium alloy are liquid at room temperature. When spiked with aluminum grains and immersed in a solution of NaOH, the droplets change shape and move in a random fashion. This video delves into the phenomenon, describing how a chemical reaction with the aluminum grains changes the local surface tension and creates Marangoni flows that make the droplets move. To get the droplet motion, you need to have the aluminum concentration just right. With too little, there’s not enough Marangoni flow. With too much, the hydrogen gas produced in the chemical reaction disrupts the droplet motion. (Video and image credit: N. Kim)
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Inside Cuttlefish Suction
Cuttlefish, like many cephalopods, catch prey with their tentacles. Suction cups along the tentacle help them hold on. In this video, researchers share preliminary studies of what goes on inside these suction cups as they’re detached. The low pressures inside the suction cup cause water to vaporize, temporarily. As seen for both the cuttlefish and a bio-inspired suction cup, small bubbles form inside the attached cup, coalesce into larger bubbles, and then get destroyed in the catastrophic leak that occurs once part of the suction cup detaches. (Video and image credit: B. Zhang et al.)
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La Grande Dune du Pilat
Southwest of Bordeaux in France stands Europe’s tallest sand dune, La Grande Dune du Pilat. Some 2.7 kilometers long and over 100 meters high, this dune took shape here over thousands of years. It moves inland a few meters every year as winds blowing from the Atlantic push sand up its shallow seaward side to the dune’s crest. There, sand will avalanche down the steeper leeward side, advancing the dune little by little. The dune’s accumulation has not been steady; during cooler and drier times, sand has collected there, but it took warmer and wetter climes to grow the forests that have helped stabilize the soil and build the dune higher. Humanity has played a role as well, at times introducing new tree species to stabilize the dune. (Image credit: W. Liang; via NASA Earth Observatory)
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Bright Night Lights
A coronal mass ejection from the Sun set night skies ablaze in mid-October 2024. This composite panorama shows a busy night sky over New Zealand’s South Island. A widespread red aurora was joined by a green picket-fence aurora and a host of other magnetohydrodynamic phenomena. To the left shines a bright Stable Auroral Red (SAR) arc. On the right near the Moon hangs the purple arc of a STEVE — strong thermal emission velocity enhancement. All of these auroras (and aurora-adjacent phenomena) take place when high-energy particles from the solar wind interact with molecules in our atmosphere. Which molecules they encounter determines the color of the aurora, and the shape depends, in part, on which magnetic lines the particles get funneled down. With strong solar storms like this one, auroras can reach far from the poles, and, as seen here, can show up in many varieties. (Image credit: T. McDonald; via APOD)
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