extraposition of subjects

Actually, English speakers don't often place that clauses in subject position even though such sentences are entirely grammatical More often we move such clausal subjects to the end of the sentence replacing them with the pronoun it. 

This process is called extraposition. 

Normally, it has anaphoric reference, i.e. it refers to an entity that has already been introduced into the discourse Here, however, it has cataphoric reference; its referent is a clause that appears later in the utterance.

It was astonishing that the burglary had not been discovered.