nadir vs celestial sphere

nadir and celestial sphere both are nouns.

Word	Noun	Adjective	Verb	Adverb
nadir	Yes	No	No	No
celestial sphere	Yes	No	No	No

nadir (noun)	celestial sphere (noun)
the point below the observer that is directly opposite the zenith on the imaginary sphere against which celestial bodies appear to be projected	the apparent surface of the imaginary sphere on which celestial bodies appear to be projected
an extreme state of adversity; the lowest point of anything