Analyse almost astronomical distance (5)
I believe the answer is:
parse
'analyse' is the definition.
(parsing is a kind of analysing)
'almost astronomical distance' is the wordplay.
'almost' means to remove the last letter (most of the word but not all of it).
'astronomical distance' becomes 'parsec' (I've seen this before).
'parsec' with its final letter removed is 'PARSE'.
(Other definitions for parse that I've seen before include "Deconstruct grammatically" , "Analyse sentence" , "Resolve (a sentence) into its constituent parts" , "Resolve the structure of a sentence" , "Analyse grammatically" .)