astronomer vs Galileo Galilei

astronomer and Galileo Galilei both are nouns.

Word	Noun	Adjective	Verb	Adverb
astronomer	Yes	No	No	No
Galileo Galilei	Yes	No	No	No

astronomer (noun)	Galileo Galilei (noun)
a physicist who studies astronomy	Italian astronomer and mathematician who was the first to use a telescope to study the stars; demonstrated that different weights descend at the same rate; perfected the refracting telescope that enabled him to make many discoveries (1564-1642)