A twilight phenomenon is produced when exhaust particles from propellant left in the vapor trail of a spaceship condense, freeze, and then expand in the less dense upper atmosphere. The exhaust plume is then illuminated by high altitude sunlight.

A twilight phenomenon is produced when exhaust particles from propellant left in the vapor trail of a spaceship condense, freeze, and then expand in the less dense upper atmosphere. The exhaust plume is then illuminated by high altitude sunlight.