(Image: NASA)
IT鈥橲 like threading a needle while travelling faster than the speed of sound. Pilots at the US air force test pilot school flew this supersonic T-38C jet to the right place at the right time so that NASA could capture this photograph of the jet鈥檚 shock waves. When the waves are forced together, they merge into one, creating a sonic boom.
Advertisement
This is the first time shock waves have been photographed from the ground in such detail. The technique takes advantage of the sun both as a very bright light source and as a background. Edward Haering at NASA鈥檚 Armstrong Flight Research Center in California and his team used a special optical filter to reveal the sun鈥檚 textured surface, stippled with sunspots. This meant the team could make hundreds of detailed observations of each shock wave by observing how it distorted the pattern of sunspots.
(Image: NASA)
Skilful flying was needed to get the photo: the jet had to be within 90 metres of a specific point in the sky between the camera and the sun in a 2 minute window. Had it missed, the sun鈥檚 position in the sky would have changed because of Earth鈥檚 rotation and the opportunity would have gone.
The technique is called Background-Oriented Schlieren using Celestial Objects. Schlieren photography (from the German for 鈥渟treak鈥�) was developed in the 1860s to visualise air flow around a moving object. The new method could also be used to take photos silhouetted against the pocked surface of the moon.
This article appeared in print under the headline 鈥淪hock wave silhouette鈥�
