。
Dawn is about to break.
Literal
Night [subj-が] open-[volitional-よう]-doing.
~ようとしている ('be about to X, be on the verge of X') is a formal progressive-with-intent construction. Built from the volitional form + とする ('try to do') + ている. Used for imminent events as well as actual intentions. Here with 明ける ('break (of dawn)').