Petition stars outside entrance to show (6)
I believe the answer is:
orison
'petition' is the definition.
('orison' can be a synonym of 'petition')
'stars outside entrance to show' is the wordplay.
'stars' becomes 'orion' (I've seen this before**).
'outside' means one lot of letters goes inside another.
'entrance to' indicates taking the first letters.
The first letter of 'show' is 's'.
'orion' placed around 's' is 'ORISON'.
(Other definitions for orison that I've seen before include "Supplication" , "Prayer - O no sir! (anag)" , "An archaic or literary prayer" , "O, no, sir, it makes a prayer" .)