nadir vs celestial point

nadir and celestial point both are nouns.

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

As nouns, celestial point is a hypernym of nadir; that is, celestial point is a word with a broader meaning than nadir:

nadir: the point below the observer that is directly opposite the zenith on the imaginary sphere against which celestial bodies appear to be projected
celestial point: a point in the heavens (on the celestial sphere)

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