The sun's course and the greatness of the lights
Basil is explaining the fourth day's creation of the sun and moon, arguing that their size is absolute, not merely relative to smaller stars.
All these things happen when the sun has already passed by toward the northern region. From these facts one can infer how great the burning is that the sun's ray produces in the air, and what kinds of effects it brings about. Then the season of autumn receives us, and it breaks down the excess of the stifling heat. Little by little it lets up on the warmth, and through the moderate mean of its mixture it leads us unharmed through itself into winter—clearly because the sun is turning back again from the northern regions toward the south. These turnings of the seasons, which follow the movements of the sun, order our life for us.
But let them be, Scripture says, also for days—not so as to make days, but so as to rule over the days. For day and night are older than the creation of the lights. The psalm shows us this when it says: He set the sun for authority over the day, the moon and stars for authority over the night (Psalm 135:8-9 LXX; Hebrew 136:8-9). How then does the sun have authority over the day? Because it carries light in itself, and whenever it rises above our horizon, it provides day by dissolving the darkness. So no one would go wrong in defining day as the air illuminated by the sun, or in defining day as a measure of time in which the sun spends its course in the hemisphere above the earth.
But the sun and moon were also appointed for years. The moon, whenever it completes its own course twelve times, produces a year—except that it often needs an intercalary month for the exact convergence of the seasons, as the Hebrews of old reckoned the year, and the most ancient of the Greeks. A solar year is the return of the sun by its own movement from the same point back to the same point.
And God made the two great lights. Since the word great in one sense has an absolute meaning—as in great is the heaven, and great is the earth, and great is the sea—but in most cases it naturally refers to something else—as in great is the horse, and the ox is great, for such things receive their testimony of greatness not in the excess of their bodily bulk but in comparison with things like themselves—how then shall we understand the meaning of great? Is it as when we call the ant or some other naturally small thing great, testifying to its superiority by comparison with things of the same kind? Or is great used here in such a way that the greatness is displayed in the very construction of the lights themselves? I think the latter. For they are not great because they are larger than the smaller stars, but because their circumference is so vast that the radiance poured out from them is sufficient to illuminate both heaven and the air, and at the same time to extend over all the earth and the sea. Since they appear in every part of the heaven, rising and setting and holding the middle, they show themselves equal to human beings from every direction. This is clear proof of the abundance of their greatness: the breadth of the earth causes no variation in them so that they seem larger or smaller.
Greek
Ταῦτα δὲ πάντα πρὸς τὸ βόρειον μέρος παροδεύσαντος ἤδη γίνεται τοῦ ἡλίου. Ἐκ δὲ τούτων εἰκάζειν ἐστὶ τὴν ἐκ τῆς ἡλιακῆς ἀκτῖνος ἐγγινομένην πύρωσιν τῷ ἀέρι, ὅση τίς ἐστι, καὶ ποταπῶν ἀποτελεστικὴ συμπτωμάτων. Ἐντεῦθεν διαδεξαμένη ἡμᾶς τοῦ μετοπώρου ἡ ὥρα, ὑποθραύει μὲν τοῦ πνίγους τὸ ὑπερβάλλον, κατὰ μικρὸν δὲ ὑφιεῖσα τῆς θέρμης, διὰ τῆς κατὰ τὴν κρᾶσιν μεσότητος ἀβλαβῶς ἡμᾶς δι' ἑαυτῆς τῷ χειμῶνι προσάγει· δηλονότι τοῦ ἡλίου πάλιν ἀπὸ τῶν προσαρκτίων ἐπὶ τὰ νότια ὑποστρέφοντος. Αὗται τῶν ὡρῶν αἱ περιτροπαὶ, ταῖς κινήσεσιν ἑπόμεναι τοῦ ἡλίου, τὸν βίον ἡμῖν οἰκονομοῦσιν. Ἔστωσαν δὲ, φησὶ, καὶ εἰς ἡμέρας· οὐχ ὥστε ἡμέρας ποιεῖν, ἀλλ' ὥστε κατάρχειν τῶν ἡμερῶν. Ἡμέρα γὰρ καὶ νὺξ πρεσβύτερα τῆς τῶν φωστήρων γενέσεως. Τοῦτο γὰρ ἐνδείκνυται ἡμῖν καὶ ὁ ψαλμὸς λέγων· Ἔθετο ἥλιον εἰς ἐξουσίαν τῆς ἡμέρας, σελήνην καὶ ἀστέρας εἰς ἐξουσίαν τῆς νυκτός. Πῶς οὖν ἔχει τὴν ἐξουσίαν τῆς ἡμέρας ὁ ἥλιος; Ὅτι τὸ φῶς ἐν ἑαυτῷ περιφέρων, ἐπειδάν ποτε τὸν καθ' ἡμᾶς ὁρίζοντα ὑπεράρῃ, ἡμέραν παρέχει διαλύσας τὸ σκότος. Ὥστε οὐκ ἄν τις ἁμάρτοι, ἡμέραν ὁρισάμενος εἶναι τὸν ὑπὸ τοῦ ἡλίου πεφωτισμένον ἀέρα· ἢ, ἡμέραν εἶναι χρόνου μέτρον ἐν ᾧ ἐν τῷ ὑπὲρ γῆν ἡμισφαιρίῳ ὁ ἥλιος διατρίβει. Ἀλλὰ καὶ εἰς ἐνιαυτοὺς ἐτάχθησαν ἥλιος καὶ σελήνη. Σελήνη μὲν ἐπειδὰν δωδεκάκις τὸν ἑαυτῆς ἐκτελέσῃ δρόμον, ἐνιαυτοῦ ἐστι ποιητική· πλὴν ὅτι μηνὸς ἐμβολίμου δεῖται πολλάκις πρὸς τὴν ἀκριβῆ τῶν ὡρῶν συνδρομήν, ὡς Ἑβραῖοι τὸ παλαιὸν τὸν ἐνιαυτὸν ἦγον καὶ τῶν Ἑλλήνων οἱ ἀρχαιότατοι. Ἡλιακὸς δέ ἐστιν ἐνιαυτὸς ἡ ἀπὸ τοῦ αὐτοῦ σημείου ἐπὶ τὸ αὐτὸ σημεῖον κατὰ τὴν οἰκείαν κίνησιν τοῦ ἡλίου ἀποκα τάστασις. 6.9 Καὶ ἐποίησεν ὁ Θεὸς τοὺς δύο φωστῆρας τοὺς μεγάλους. Ἐπειδὴ τὸ μέγα τὸ μὲν ἀπόλυτον ἔχει τὴν ἔννοιαν· ὡς μέγας ὁ οὐρανὸς, καὶ μεγάλη ἡ γῆ, καὶ μεγάλη ἡ θάλασσα· τὰ δὲ ὡς τὰ πολλὰ πέφυκε πρὸς ἕτερον ἀναφέ ρεσθαι· ὡς μέγας ὁ ἵππος, καὶ ὁ βοῦς μέγας (οὐ γὰρ ἐν τῇ ὑπερβολῇ τῶν τοῦ σώματος ὄγκων, ἀλλ' ἐν τῇ πρὸς τὰ ὅμοια παραθέσει τὴν μαρτυρίαν τοῦ μεγέθους τὰ τοιαῦτα λαμβάνει)· πῶς τοίνυν τοῦ μεγάλου τὴν ἔννοιαν ἐκδεξόμεθα; Πότερον ὡς τὸν μύρμηκα, ἢ ἄλλο τι τῶν φύσει μικρῶν, μέγα προσαγορεύομεν διὰ τὴν πρὸς τὰ ὁμογενῆ σύγκρισιν τὴν ὑπεροχὴν μαρτυροῦντες; ἢ τὸ μέγα νῦν οὕτως, ὡς ἐν τῇ οἰκείᾳ τῶν φωστήρων κατασκευῇ τοῦ μεγέθους ἐμφαινομένου; Ἐγὼ μὲν οἶμαι τοῦτο. Οὐ γὰρ ἐπειδὴ μείζους τῶν μικροτέρων ἀστέρων, διὰ τοῦτο μεγάλοι· ἀλλ' ἐπειδὴ τοσοῦτοι τὴν περιγραφὴν, ὥστε ἐξαρκεῖν τὴν ἀπ' αὐτῶν ἀναχεομένην αὐγὴν καὶ οὐρανὸν περιλάμπειν καὶ τὸν ἀέρα, καὶ ὁμοῦ πάσῃ τῇ γῇ καὶ τῇ θαλάσσῃ συμπαρεκτείνεσθαι. Οἵ γε κατὰ πᾶν μέρος τοῦ οὐρανοῦ γινόμενοι, καὶ ἀνατέλλοντες καὶ δυόμενοι καὶ τὸ μέσον ἐπέχοντες, ἴσοι πανταχόθεν τοῖς ἀνθρώποις προφαίνονται, ὅπερ ἀπόδειξιν ἔχει σαφῆ τῆς τοῦ μεγέθους περιουσίας, τῷ μηδὲν αὐτοῖς ἐπισημαίνειν τὸ πλάτος τῆς γῆς πρὸς τὸ μείζονας δοκεῖν ἢ ἐλάττονας εἶναι.