northern lights vs aurora

northern lights and aurora both are nouns.

Word	Noun	Adjective	Verb	Adverb
northern lights	Yes	No	No	No
aurora	Yes	No	No	No

As nouns, aurora is a hypernym of northern lights; that is, aurora is a word with a broader meaning than northern lights:

northern lights: the aurora of the Northern Hemisphere
aurora: an atmospheric phenomenon consisting of bands of light caused by charged solar particles following the earth's magnetic lines of force

northern lights (noun)	aurora (noun)
the aurora of the Northern Hemisphere	an atmospheric phenomenon consisting of bands of light caused by charged solar particles following the earth's magnetic lines of force
	the first light of day