Mope around film location when heavenly body disappears (7)
I believe the answer is:
moonset
'mope around film location' is the definition.
The definition suggests a singular noun which matches the answer.
'heavenly body disappears' is the wordplay.
'heavenly body' becomes 'moon' (moon is a kind of heavenly body).
'disappears' becomes 'set' (I can't explain this - if you can you should believe this answer much more).
'moon'+'set'='MOONSET'
'when' acts as a link.
Can you help me to learn more?
(Other definitions for moonset that I've seen before include "When Earth's satellite disappears below the horizon" , "when night becomes even darker?" , "Going down of Earth's satellite" , "disappearance of satellite" , "astronomical activity" .)