When prepping to watch an eclipse, one thing space agencies can’t say enough is not to stare directly at the sun. And yet, that’s exactly what NASA scientists have been doing, and none of it has anything to do with astronomical research.
What the scientists are actually doing is studying the shockwave emitted by a supersonic jet as it breaks the sound barrier. They do this by reinventing a century-old photography technique and using the sun itself as a backdrop.
Schlieren imaging, as it’s called, was invented by a German physicist in the 19th century as a way to capture supersonic objects. This is done by photographing the ripples they make in the air when backlit by uniform illumination. NASA’s Background Oriented Schlieren using Celestial Objects (BOSCO) technique instead uses the sun itself as a background, and even makes it possible to track from a plane 10,000 feet in the air. To survive being pointed directly at the sun, the cameras have to use a special hydrogen alpha filter, which only allows specific wavelengths of light through.
All of this is in the hopes that observing the sonic booms can help scientists devise ways to eliminate that pesky phenomenon. Why you ask? If that happens, supersonic jets could then fly closer to the Earth’s surface, and even do overland routes with no worries of causing damage to people or property in the flight path. In turn, this could cut down supersonic flight times by half, and maybe even make them commercially viable.