Aspect true of the stars? (8)
I believe the answer is:
sidereal
'of the stars?' is the definition.
(I've seen this before)
'aspect true' is the wordplay.
'aspect' becomes 'side' (side is a kind of aspect).
'true' becomes 'real' ('real' can be similar in meaning to 'true').
'side'+'real'='SIDEREAL'
(Other definitions for sidereal that I've seen before include "Like stars" , "Relating to the distant stars" , "Full of stars" , "Of the stars or constellations" , "involving stars" .)