From the Astronomy Picture of the Day for 2003 May 4 - A Sonic Boom.

Many people have heard a sonic boom, but few have seen one. When an airplane travels at a speed faster than sound, density waves of sound emitted by the plane cannot precede the plane, and so accumulate in a cone behind the plane. When this shock wave passes, a listener hears all at once the sound emitted over a longer period: a sonic boom. As a plane accelerates to just break the sound barrier, however, an unusual cloud might form…

… and that’s One to Grow On.

The bit over the canopy is a second wave forming.

On Shuttle the tail is outside of the wavefront formed by the vehicle's nose and it forms it's own wave and it is one of the few times you'll hear a double sonic boom when it goes overhead.