southern lights vs aurora australis

southern lights and aurora australis both are nouns.

Word	Noun	Adjective	Verb	Adverb
southern lights	Yes	No	No	No
aurora australis	Yes	No	No	No

As nouns, southern lights and aurora australis are synonyms defined as:

southern lights and aurora australis: the aurora of the Southern Hemisphere

southern lights (noun)	aurora australis (noun)
the aurora of the Southern Hemisphere	the aurora of the Southern Hemisphere