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 .