After sunset on the ground, a rocket launch can create a giant glowing shape in the sky that looks like a jellyfish. What causes this phenomenon?

Answer: Sunlit exhaust spreading in thin high-altitude air

A special blue flame engines use after sunset — Wrong. Engine color can vary, but the giant sky-wide shape is not a special night flame. The glow mainly comes from the plume being lit by the Sun high above Earth.

A sign the rocket is already in outer space — Wrong. It is not “space glow.” The effect can happen while the rocket is still climbing, as long as the exhaust is high enough to catch sunlight above the dark ground.

Sunlit exhaust spreading in thin high-altitude air ✓ — Correct! After sunset on the ground, the rocket’s exhaust can still be high enough to catch direct sunlight. In thin air it spreads out and scatters that light, creating the giant glowing jellyfish.