Early on Thursday morning, May 5, a camera in Waycross, Georgia, witnessed a mysterious object hovering in the sky. Followed by a bright, fast, and glowing rectangular aura, the object looked a bit like a space jellyfish. Chris Combs, professor of aerodynamics and mechanical engineering at the University of Texas at San Antonio, posted the footage on Twitter.
Of course, as Combs pointed out, this space jellyfish was not a UFO. It was a SpaceX Falcon 9 rocket launched from Florida’s Kennedy Space Center, about 400 kilometers south of where the camera was deployed. Dozens of rockets are launched from the ramp at Kennedy each year, several of which cause a similar appearance to the sky with bioluminescent invertebrates.
You can watch the video in question here:
The long, swollen “body” of the jellyfish is exhaust gas from the Falcon 9’s rocket engine, Combs notes. The reason why the exhaust takes such a bulging shape has to do with the pressure difference inside and outside the engine. In this case, the exhaust from the rocket “expands less,” meaning the exhaust is at a higher pressure than the ambient air around the gas as it exits the engine.
In under-expanded exhaust you get expansion fans at the nozzle exit to decrease pressure and match background: jellyfish, at high altitude
In over-expanded exhaust you get shock waves to increase pressure back up to background: shock diamonds, lower altitude pic.twitter.com/kRGNVr2EYZ
— Chris Combs (@DrChrisCombs) September 22, 2021
The explanation for the flare is timing. As the rocket launch occurs in the predawn hours (around 5:45 pm local time) on Thursday morning, light from the Sun reaches the exhaust plume just beyond the horizon and illuminates it, causing it to shine brightly in the dark sky.
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