What causes the space jellyfish effect?
A space jellyfish appears when a rocket launches just after sunset or before sunrise. The ground is already dark, but high up, the rocket’s exhaust plume is still lit by the sun. As the air thins, the plume spreads out into a huge glowing cloud with trailing strands, like a jellyfish drifting across the sky.
Dark on the ground, sun up high
Right after sunset the sun is below your horizon, so the ground and the lower sky are dark. But tens of kilometers up, the sun is still shining. A rocket launched at this time climbs from darkness into sunlight.
Share this stepThe exhaust balloons in thin air
Near the ground, the exhaust stays a narrow trail. Higher up there’s far less air pressing on it, so the gas expands into a wide cloud. The rocket’s different engine stages and its changing speed shape it into a bell with long strands.
Share this stepSunlight makes it glow
The plume is made of gas, water vapor and tiny ice crystals. Lit by the sun against a dark sky, it glows blue and white, often for several minutes after the rocket itself has gone out of sight.
Share this stepA rocket trail lit by a sun you can’t see.
Twilightrocket exhaustglowing jellyfish
The effect has become common as launches have increased. It can be seen hundreds of kilometers away, and it’s sometimes mistaken for a UFO.
Common follow-up questions
When can you see a space jellyfish?
Only when a rocket launches within about an hour after sunset or before sunrise, and the sky is clear where you are.
Is it dangerous?
No. It’s ordinary rocket exhaust far above the ground, lit by sunlight. It drifts apart and disappears within minutes.
Why is it blue?
Sunlight scatters off the tiny ice crystals and particles in the plume, and against the darkening sky the scattered light looks blue and white.
Can other things look like this?
Yes. Missile tests and high-altitude experiments can create similar glowing clouds. Noctilucent clouds, glowing high clouds on summer nights, are lit by the sun in the same way.
