Of the stars in a past rally (6)
I believe the answer is:
astral
'of the stars' is the definition.
(relating to stars or astronomy)
'in a past rally' is the wordplay.
'in' says the answer is hidden in the clue.
'ASTRAL' is hidden in the letters of 'past rally'.
(Other definitions for astral that I've seen before include "19 [STELLAR]" , "To do with stars on altars" , "Altars (anag)" , "Resembling the stars - of the spirit world" , "Characteristic of stars" .)