Josiah Renick Smith, Xenophon: Memorabilia

ὁ μὲν ἥλιος, ἡ δὲ νύξ: while the sum, yet the night. Both clauses are grammatically equivalent parts of the general reason introduced by ἐπειδή, but the weight of the reason lies in ἡ δὲ νὺξ κτλ.

τάς τε ὥρας τῆς ἡμέρας: for the divisions of the day, see on i.1.10.

διὰ τὸ σκοτεινὴ εἶναι: change in form of expression from φωτεινὸς ὤν above. For the case of σκοτεινή, see on αὐτός ii. 3. 11.

ἀνέφηναν: caused to shine.

τῆς νυκτὸς τὰς ὥρας: the Greeks divided the night into three watches (φυλακαί), the Romans into four (vigiliae).

διὰ τοῦτο: by means of this, refers to ἄστρα ... ἀνέφηναν.

πολλὰ πράττομεν: sc. which we could not do but for the help of moonlight and starlight.

τοῦ μηνὸς τὰ μέρη: the month had three divisions, the first and last of which were called ἱσταμένου and φθίνοντος (μηνός), the days of the middle division being reckoned as πρώτη ἐπὶ δέκα etc. The average length of a lunar month is a little over twenty-nine and a half days; the Greeks took it at exactly twentynine and a half days, and avoided the fraction by making one month of twenty-nine days and the next of thirty. See Gow, Companion to School Classics, p. 79.