A heavenly body appearing in religious texts (6)
I believe the answer is:
avesta
'religious texts' is the definition.
(I've seen this before)
'a heavenly body' is the wordplay.
'heavenly body' becomes 'vesta' (I've seen this before).
'a'+'vesta'='AVESTA'
'appearing in' acts as a link.
(Other definitions for avesta that I've seen before include "Zoroastrian scriptures" , "collection of holy writings" , "sacred text" , "Parsee scriptures" , "holy text" .)