aurora vs break of the day

aurora and break of the day both are nouns.

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

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

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

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