וַיִּקְרָ֧א אֱלֹהִ֛ים לָֽרָקִ֖יעַ שָׁמָ֑יִם וַֽיְהִי־עֶ֥רֶב וַֽיְהִי־בֹ֖קֶר י֥וֹם שֵׁנִֽי׃ (פ)
And God called the firmament Heaven. And there was evening and there was morning, a second day.
Read kabbalistic (mystical) interpretation of Genesis 1:8: and classical mystical sources.