German dons behind blue atmospheric phenomenon (9)
I believe the answer is:
afterglow
'atmospheric phenomenon' is the definition.
(afterglow is a kind of atmospheric phenomenon)
I don't understand how the remainder of the clue works.
Can you help me to learn more?
(Other definitions for afterglow that I've seen before include "Post-sunset radiance" , "Remaining light" , "appearing when sun has set?" , "residual light" , "Light once the actual source has gone" .)