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. The origin of this cloud is still debated. A leading
theory is that a drop in air pressure at the plane described by the Prandtl-Glauert
Singularity occurs so that moist air condenses there to form water droplets. Above,
an F/A-18 Hornet was photographed just as it broke the sound barrier. Large meteors
and the space shuttle frequently produce audible sonic booms before they are slowed
below sound speed by the Earth's atmosphere.