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.
In aerodynamics, the sound barrier usually refers to the
point at which an aircraft moves from transonic to supersonic
speed. The term came into use during World War II when
a number of aircraft started to encounter the effects
of compressibility, a grab-bag of unrelated aerodynamic
effects. By the 1950s, aircraft started to routinely "break"
the sound barrier.
The white halo is formed by condensed water droplets which
are thought to result from a drop in air pressure around
the aircraft...
