Starry cast rally, though not all (6)
I believe the answer is:
astral
'starry' is the definition.
(astral means relating to stars)
'cast rally though not all' is the wordplay.
'not all' indicates the answer is hidden within the clue.
'ASTRAL' is hidden within 'cast rally though'.
(Other definitions for astral that I've seen before include "Pertaining to the stars" , "Resembling the stars - of the spirit world" , "Universal" , "Related to the stars" , "Like the stars" .)