The Falcon Heavy Nebula occurs when two side boosters initiate a “Boostback Burn” to fly themselves back to their launch site. In the upper atmosphere the air is thin, and that allows flames from the rocket engines to expand instead of shooting straight down, as they would at liftoff. The Nebula occurs when flames from these boosters interact at night, illuminating the surrounding plumes of hot gases.
It's also insanely beautiful.
This free download can be printed oversize at 24"x36"
Photo by the talented Erik Kuna.