Before the eclipse this summer, NASA warned us over and over again not to stare directly at the sun — but now they’re doing just that. Its researchers have reinvented a photography technique more than a century old, using the sun itself as a backdrop[1] in order to capture the shockwave produced by a new supersonic jet.
Schlieren imaging was invented by a German physicist in the 19th century as a way to capture objects moving at supersonic speeds; it basically works by tracking tiny distortions to a uniform background illumination that are produced when the air is disturbed by a passing object.
The results are striking and you’ve likely seen them before. But traditional Schlieren imaging is limited in its range and scale; NASA’s Background Oriented Schlieren using Celestial Objects (BOSCO) allows the sun itself to be used as the background, and not only that, but it’s reliable enough to be used from a chaser plane 10,000 feet up.
Another Schlieren photo from NASA that uses the edge of the sun as its uniform background; BOSCO uses the disc itself.
Previous background oriented Schlieren imaging efforts for viewing the distortion patterns of planes in flight have been shot top-down with a featureless landscape as their background, or bottom-up using the edge of the sun (as you see above). But BOSCO aims its telescopic camera directly at the disc of the sun, capturing the aircraft as it causes a partial, highly local eclipse.
In order not to be completely blown out, the camera system uses a “hydrogen alpha filter,” which only lets in a very specific wavelength of light, which is produced by the sun in a nice granular pattern.
You can see it in action...