The Prandtl–Glauert singularity (sometimes referred to as a "vapor cone"), is the point at which a sudden drop in air pressure occurs, and is generally accepted as the cause of the visible condensation cloud that often surrounds an aircraft traveling at transonic speeds, though there remains some debate. It is an example of a mathematical singularity in aerodynamics.
These condensation clouds, also known as "shock collars" or "shock eggs," are frequently seen during Space Shuttle launches around 25 to 33 seconds after launch when the vehicle is traveling at transonic speeds. These effects are also visible in archival footage of some nuclear tests.
