polar star vs Ursa Minor

polar star and Ursa Minor both are nouns.

Word	Noun	Adjective	Verb	Adverb
polar star	Yes	No	No	No
Ursa Minor	Yes	No	No	No

polar star (noun)	Ursa Minor (noun)
the brightest star in Ursa Minor; at the end of the handle of the Little Dipper; the northern axis of the earth points toward it	a constellation outside the zodiac that rotates around the North Star, also known as the Little Bear or Little Dipper