Like a clear, moonless night when the last rays linger (6)
I believe the answer is:
starry
'like a clear moonless night' is the definition.
I know that 'night' relates to this answer.
'the last rays linger' is the wordplay.
'the last rays' becomes 's' (I am not sure about this - if you are sure you should believe this answer much more).
'linger' becomes 'tarry' (synonyms).
's'+'tarry'='STARRY'
'when' acts as a link.
Can you help me to learn more?
(Other definitions for starry that I've seen before include "like Hollywood Boulevard?" , "with many famous actors" , "Like the optimist's eyes or the sky at night" , "Like the Milky Way" , "Of celebrities" .)