01 — Approach
The pile-up
Below the barrier, pressure waves race ahead and warn the air to part. Near Mach 1 they can't outpace the body: they crowd into a thin, near-vertical bow shock that stands just off the nose.
Reading the density
Sound travels at one speed. Force a body past it and the air has nowhere to send the news — so it stacks.
02 — Crossing
The collar
Air accelerating over the body expands, cools, and — for a held breath at transonic speed — drops below its dew point. A condensation collar of vapour flashes into being, then is gone.
03 — Beyond
The cone
Supersonic, every disturbance is trapped inside a trailing Mach cone. Its half-angle μ = arcsin(1/M) narrows as the body goes faster — the geometry you hear later as the boom.