date of reference vs astronomy

date of reference and astronomy both are nouns.

Word	Noun	Adjective	Verb	Adverb
date of reference	Yes	No	No	No
astronomy	Yes	No	No	No

date of reference (noun)	astronomy (noun)
(astronomy) an arbitrarily fixed date that is the point in time relative to which information (as coordinates of a celestial body) is recorded	the branch of physics that studies celestial bodies and the universe as a whole