Writer's uplifting music for 'Heavenly Body' (7)
I believe the answer is:
neptune
'for heavenly body' is the definition.
(Neptune is an example)
'writer's uplifting music' is the wordplay.
'writer' becomes 'pen' (something which writes).
'uplifting' says the letters should be written in reverse.
'music' becomes 'tune' (tune is a kind of music).
'pen' backwards is 'nep'.
'nep'+'tune'='NEPTUNE'
(Other definitions for neptune that I've seen before include "Holst composed it" , "Remote planet" , "part of Planets Suite" , "World" , "in Holst's suite" .)