Category: Phenomena

Understanding Schlieren
Schlieren techniques are one of my favorite forms of flow visualization. They cleverly make the invisible visible through an optical set-up that’s sensitive to changes in density. They’re great–as seen in the examples here–for seeing local buoyant flows like the plumes that rise from a candle, or for making gases like carbon dioxide visible. They’re also excellent for visualizing shock waves.
In this video, physicist David Jackson explains how one particular flavor of schlieren–one using a spherical mirror–works. There are lots of other possible schlieren set-ups, too, though each one has its quirks. (Video and image credit: All Things Physics; submitted by David J.)
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February 26, 2026
Connecting Canals
Before the rise of railroads, canals provided critical commercial shipping infrastructure for many locations worldwide. But connecting canals at different elevations required locks–sometimes a whole series of them–as in the case of Scotland’s Union Canal and the Forth and Clyde Canal. In the canals’ heyday, navigating the 11 locks between them took the better part of a day–one of many reasons that canals fell out of use over time.
When Scotland decided to reconnect the canals in the 1990s, they picked a very different solution for this elevation challenge: the Falkirk Wheel. Grady walks us through the clever engineering of this impressive piece of infrastructure in this Practical Engineering video. (Video and image credit: Practical Engineering)
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February 25, 2026
Inside Cepheid Variable Stars
Cepheid variable stars pulsate in brightness over regular periods. That’s one reason astronomers use them as a standard candle to judge distances–even for stars well outside our galaxy. In this image, researchers display a simulation of convection inside a Cepheid eight times more massive than our sun. The colors represent vorticity, with zero vorticity in white.(Image credit: M. Stuck and J. Pratt)
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February 24, 2026
Recreating Atmospheric Rivers
During the winter months, those of us living in the mid-latitudes sometimes experience atmospheric rivers. Formed from the interaction of cold winter storms with warm, moist tropical air, atmospheric rivers can deliver intense rainfall across long distances. In this video, the UCLA SpinLab team shows how you can recreate the effect with a relatively simple and affordable DIYnamics apparatus. (Video and image credit: UCLA SpinLab)
February 23, 2026
Sprites and ELVES
Although we are most familiar with the white, branching lightning caused by electrical discharge between clouds and the ground, there are many types of lightning. This fortuitous image captures two: tentacled red sprites and ring-like ELVES. Sprites extend upward from the top of a thunderstorm, in a large but weak flash that lasts only seconds. ELVES appear as a rapidly-expanding disc, thought to be caused by an energetic electromagnetic pulse moving into the ionosphere. They were first discovered in footage from a 1992 Space Shuttle mission. (Image credit: V. Binotto; via APOD)
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February 19, 2026
“Broken Water, Like Broken Glass”
How can you break water? By accelerating it so quickly that the pressure drop forms cavitation bubbles. Here, a steel piston rests against a transparent plate, all underwater. When a hammer strike accelerates the piston away at around 1000g, the severe pressure drop tears the water into bubbles (bottom, left). As the bubbles expand, the nearby piston squishes them into pancakes (bottom, center). As they continue growing, the bubbles press into one another, squeezing thin ridges of water between them. The result (center) resembles broken glass. (Image credit: J. da Silva et al.)
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February 18, 2026
Milano Cortina 2026: Speedskating Team Pursuit
Track cycling and speedskating often mirror one another, with similar events in each sport. In the team pursuit, for example, cyclists and skaters compete as a team to post the fastest time for a given distance. In cycling events, riders spend the race tucked into a line, with the lead rider providing a draft for their teammates. But that’s a tiring position for a cyclist, so every few laps the lead rider will pull off, move up the track, and drop behind their teammates for a rest. Speedskaters used to use the same technique. But no longer.
After working with aerodynamic simulation specialists, U.S. Speedskating pioneered a new race technique, in which skaters never change positions. Instead, each racer specializes in one position and skates while pushing the skater ahead of them. The technique requires a lot of practice, finesse, and trust; skaters in the later positions cannot see, skating as close as they can to the skater in front of them.
But, performance-wise, the new technique works. It’s taken U.S. women’s team pursuit from eighth in the world to number one. Other teams have adopted the technique, too, so this is likely what team pursuit will look like in the years to come. (Image credits: various, see image captions; via NPR)
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February 17, 2026
A Bubbly Heart
Next time you fill your water bottle, watch closely and see if you can spot a bubble heart like these. When a jet falls into a pool, it pulls air in with it. The low pressure of the jet pulls bubbles inward, even as shear pulls the bubbles downward with the sinking liquid. If the bubbles are large and there’s enough momentum in the jet, the lower portion of the bubble will get pulled into a conical shape, while the upper portion remains a hemisphere. That forms one lobe of the heart. The other half requires a second bubble. But with a little patience and luck, you can form a complete heart. Happy Valentine’s Day! (Image credit: S. Tuley et al.)
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February 13, 2026
Milano Cortina 2026: How Ski Skins Work
The 2026 Olympics include the debut of ski mountaineering (a.k.a. skimo), a sprint race heading both up and down the mountain on skis. During the uphill segment of the race, competitors use skins on their skis to help them climb; these skins then get ripped off (see below) before skiing back down.
As their name suggests, the first climbing skins used on skis were made from seal skin. By angling the seal fur, skiers could glide in the forward direction and resist sliding backwards. Modern skins may have animal or synthetic fibers, but they use the same physical mechanism. The angled hairs let skis slide forward easily, then grip and resist sliding backward. (Image credits: touring – H. Morkel, skins – Josefka, video – NBC Bay Area)
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February 12, 2026
Milano Cortina 2026: Cortina Sliding Center
This year’s sliding events–bobsleigh, luge, and skeleton–will take place at the brand-new Cortina Sliding Center. Built on the site of a historic sliding track, this new venue came together in only the last couple of years. It features a state-of-the-art refrigeration system that pumps a mixture of water and ethylene glycol beneath the track surface to keep the ice properly chilled. Each section of the track is continuously monitored to optimize the flow rate, temperature, and pressure of the refrigerant to keep the track at maximum performance while minimizing environmental impact.
According to the designers, it’s the first competition track to use a glycol-based refrigeration system, which should be more sustainable than the ammonia-based systems used elsewhere. For a sense of what a run is like, check out this skeleton driver POV run from the facility’s shakedown competition last year. (Image credit: LMSteel; video credit: tuff sledding)
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February 11, 2026