Is It Real or Is It Photoshop?

Muse, Apr 2004

A jet leaps through a white disk like a tiger through a paper-covered hoop. But what is the white disk? Could it be the sound barrier?

This F-18 had actually been traveling faster than the speed of sound for some time when this photo was made. When a jet is moving that fast (about 770 miles per hour), it pushes on the sound waves in front of it. But sound waves can't travel faster than the speed of sound. So they pile up against one another. These piled-up waves are called shock waves. One of them is the shape of a cone centered on the jet's nose.

Within this cone-shaped surface, the air pressure is higher than normal. But behind it the air pressure drops. When the pressure drops, the temperature drops as well. If it gets cold enough, water vapor in the air condenses into droplets-just as it does in the clouds. So as the jet roars past, making shock waves, clouds flare and dwindle, flare and dwindle in its wake. You can see this happening at www.cofc. edu/~frysingj/fs14ss.mpg. You don't have to be an airplane freak to think this is cool.