vault of heaven vs celestial sphere

vault of heaven and celestial sphere both are nouns.

Word	Noun	Adjective	Verb	Adverb
vault of heaven	Yes	No	No	No
celestial sphere	Yes	No	No	No

As nouns, vault of heaven and celestial sphere are synonyms defined as:

vault of heaven and celestial sphere: the apparent surface of the imaginary sphere on which celestial bodies appear to be projected

Other synonyms of vault of heaven include empyrean, firmament, heavens, sphere, welkin.

vault of heaven (noun)	celestial sphere (noun)
the apparent surface of the imaginary sphere on which celestial bodies appear to be projected	the apparent surface of the imaginary sphere on which celestial bodies appear to be projected