cosmologist vs stargazer

cosmologist and stargazer both are nouns.

Word	Noun	Adjective	Verb	Adverb
cosmologist	Yes	No	No	No
stargazer	Yes	No	No	No

As nouns, stargazer is a hypernym of cosmologist; that is, stargazer is a word with a broader meaning than cosmologist:

cosmologist: an astronomer who studies the evolution and space-time relations of the universe
stargazer: a physicist who studies astronomy

Other hypernyms of cosmologist include astronomer, uranologist.

cosmologist (noun)	stargazer (noun)
an astronomer who studies the evolution and space-time relations of the universe	heavy-bodied marine bottom-lurkers with eyes on flattened top of the head
	a physicist who studies astronomy
	someone indifferent to the busy world