Bottle Rocket Shock Diamonds

Mach diamonds or shock diamonds can often be seen in the exhaust of rocket engines. Here they’re shown in high-speed video of a bottle rocket’s launch. The rocket’s exhaust exits at a pressure that is higher than the surrounding atmosphere, which causes the exhaust to bulge outward and forms two expansion fans, seen in pink, to lower the pressure. The pressure actually drops too low, however, causing shock waves, seen in turquoise, to form in order to raise the exhaust’s pressure. This back-and-forth between shock waves and expansion fans continues, forming the diamond shapes we see. Each subsequent set gets weaker as the exhaust closes in on the right pressure, and ultimately the series of diamonds fades into turbulence. (Image credit: P. Peterson and P. Taylor, source)

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