break of the day vs aurora

break of the day and aurora both are nouns.

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

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

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

break of the 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