Mach cone
= Mach cone
{c}
{title2=$\sin\theta=1/M$}
The cone forming the envelope of sound wavefronts from a source moving supersonically at <Mach number> $M>1$. In the source frame the ray-velocity sphere is centered at $-Mc_0\mathbf e_x$ and has radius $c_0$. Its tangent rays make angle $\sin^{-1}(1/M)$ to the backward flight direction; all other emitted acoustic rays lie inside that cone.