Bits of film presented in middle of week showing astronomical phenomenon (7)
I believe the answer is:
eclipse
'astronomical phenomenon' is the definition.
'bits of film presented in middle of week' is the wordplay.
'bits of film' becomes 'clips' (film clips).
'presented in' is an insertion indicator.
'middle of' means to look at the middle letters.
The middle of 'week' is 'ee'.
'clips' going inside 'ee' is 'ECLIPSE'.
'showing' is the link.
(Other definitions for eclipse that I've seen before include "Throw into shade, like a heavenly body" , "Blot out" , "famous racehorse" , "Throw into obscurity, perhaps the sun" , "Surpass in achievement" .)