break of day vs aurora

break of day and aurora both are nouns.

Word	Noun	Adjective	Verb	Adverb
break of day	Yes	No	No	No
aurora	Yes	No	No	No

As nouns, break of day and aurora are synonyms defined as:

Other synonyms of break of day include break of the day, cockcrow, dawn, dawning, daybreak, dayspring, first light, morning, sunrise, sunup.

break of day (noun)	aurora (noun)
the first light of day	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