Question 1

What is a space jellyfish?

Accepted Answer

A 'space jellyfish' is a glowing, expanding cloud in a twilight sky, created when a rocket launches while the ground is dark but its high-altitude exhaust plume is still lit by the Sun. The plume fans out in the thin upper atmosphere into a jellyfish-like shape visible for hundreds of miles.

Question 2

How do you predict them?

Accepted Answer

We check every upcoming launch: if the Sun is between about 4° and 16° below the horizon at the pad at liftoff — deep twilight — the plume aloft catches sunlight against a dark sky, the recipe for a jellyfish. It also depends on the rocket and weather, so these are possibilities, not guarantees.

Question 3

Where can I see one?

Accepted Answer

Jellyfish are visible across a wide region — often several US states or countries — roughly toward the launch site. The best views are from areas already in darkness with a clear view low toward the horizon.

Space jellyfish watch

Space jellyfish watch