§1.8#2ἡμεῖς δὲ λέγωμεν ἀναλαβόντες τὴν ὑποκειμένην ἀρχὴν ἡμῖν.
But let us speak, resuming the principle assumed by us.
εἴρηται γὰρ πρότερον ὅτι τὸ ἔσχατον τοῦ λεγομένου ἀέρος δύναμιν ἔχει πυρός, ὥστε τῇ κινήσει διακρινομένου τοῦ ἀέρος ἀποκρίνεσθαι τοιαύτην σύστασιν οἴαν καὶ τοὺς κομήτας ἀστέρας εἶναί φαμεν.
For it has been said before that the outermost part of the so-called air has the power of fire, so that when the air is separated by motion, there is separated out such a condensation as we say the comets also are.
τοιοῦτον δὴ δεῖ νοῆσαι γιγνόμενον ὅπερ ἐπʼ ἐκείνων, ὅταν μὴ αὐτὴ καθʼ αὑτὴν γένηται ἡ τοιαύτη ἔκκρισις, ἀλλʼ ὑπό τινος τῶν ἄστρων ἢ τῶν ἐνδεδεμένων ἢ τῶν πλανωμένων·
We must understand, then, that something of the same sort happens as in their case, whenever such an secretion does not arise by itself, but is caused by one of the stars, either the fixed ones or the planets.
τὸτε γὰρ οὗτοι φαίνονται κομῆται διὰ τὸ παρακολουθεῖν αὐτῶν τῇ φορῇ ὥσπερ τῷ ἡλίῳ τὴν τοιαύτην σύγκρισιν, ἀφʼ ἧς διὰ τὴν ἀνάκλασιν τὴν ἅλω φαίνεσθαί φαμεν, ὅταν οὕτω τύχῃ κεκραμένος ὁ ἀήρ.
For then these appear as comets because such a condensation follows their motion, just as that kind of mixture follows the sun, from which, by reflection, we say the halo appears when the air happens to be so tempered.
ὃ δὴ καθʼ ἔνα συμβαίνει τῶν ἀστέρων, τοῦτο δεῖ λαβεῖν γιγνόμενον περὶ ὅλον τὸν οὐρανὸν καὶ τὴν ἄνω φορὰν ἅπασαν· εὔλογον γάρ, εἴπερ ἡ ἑνὸς ἄστρου κίνησις, καὶ τὴν τῶν πάντων ποιεῖν τι τοιοῦτον καὶ ἐκριπίζειν ἀέρα τε καὶ διακρίνειν διὰ τὸ τοῦ κύκλου μέγεθος.
Now, what happens in the case of a single star must be understood to happen in the case of the whole heaven and the entire upper motion; for it is reasonable that, if the motion of a single star does so, the motion of all of them also should produce some such effect, and should kindle the air and separate it because of the size of the circle.
ἀνάγκη τοί νυν τῶν αὐτῶν μεγίστων κύκλων μάλιστα τὴν μέλλουσαν τοῦτο ποιήσειν φοράν χρὴ γὰρ τοῦτο, ἵνα πολλὴ κίνησις ᾖ διὰ τὸ μέγεθος γιγνομένη καὶ πλείονα τὴν ἔξαψιν ποιήσῃ. καὶ πρὸς τούτοις ἔτι καθʼ ὃν τόπον πυκνότατα καὶ πλεῖστα καὶ μέγιστα τυγχάνουσιν ὄντα τῶν ἄστρων.
It is necessary, then, that the motion which is going to produce this should be especially that of the greatest of these circles; for this is required so that there may be a great motion produced by the size and that it may make a greater ignition, and in addition to this, moreover, in that region where the stars happen to be densest, most numerous, and greatest.
ὁ μὲν οὖν τῶν ζῳδίων διὰ τὴν τοῦ ἡλίου φορὰν καὶ τὴν τῶν πλανητῶν διαλύει τὴν τοιαύτην σύστασιν· διόπερ οἱ πολλοὶ τῶν κομητῶν ἐκτὸς γίγνονται τῶν τροπικῶν.
Now the circle of the zodiac, because of the motion of the sun and the planets, dissolves such a condensation; which is why most comets arise outside the tropics.
ἔτι δʼ οὔτε περὶ τὸν ἥλιον ὔοτε περὶ σελήνην γίγνεται κόμη· θᾶττον γὰρ διακρίνουσιν ἢ ὥστε συστῆναι τοιαύτην σύγκρισιν.
Moreover, no tail arises either around the sun or around the moon; for they separate the air more quickly than for such a mixture to condense.
οὗτος δʼ ὁ κύκλος ἐν ᾧ τὸ γάλα φαίνεται τοῖς ὁρῶσιν, ὅ τε μέγιστος ὢν τυγχάνει καὶ τῇ θέσει κείμενος οὕτως ὥστε πολὺ τοὺς τροπικοὺς ὑπερβάλλειν.
But this circle in which the Milky Way appears to observers happens both to be a greatest circle and to be so situated in position as to far exceed the tropics.
πρὸς δὲ τούτοις ἄστρων ὁ τόπος πλήρης ἐστὶν τῶν μεγίστων καὶ λαμπροτάτων, καὶ ἔτι τῶν σποράδων καλουμένων (τοῦτο δʼ ἐστὶν καὶ τοῖς ὄμμασιν ἰδεῖν φανερόν), ὥστε διὰ ταῦτα συνεχῶς καὶ ἀεὶ ταύτην πᾶσαν ἀθροίζεσθαι τὴν σύγκρισιν.
In addition to these things, the region is full of the greatest and brightest stars, and also of those called sporadic (and this is manifest even to see with the eyes), so that because of these things, this entire mixture is continuously and always gathered there.
σημεῖον δέ· καὶ γὰρ αὐτοῦ τοῦ κύκλου πλέον τὸ φῶς ἐστιν ἐν θατέρῳ ἡμικυκλίῳ τῷ τὸ δίπλωμα ἔχοντι· ἐν τούτῳ γὰρ πλείω καὶ πυκνότερά ἐστιν ἄστρα ἢ ἐν θατέρῳ, ὡς οὐ διʼ ἑτέραν τινʼ αἰτίαν γιγνομένου τοῦ φέγγους ἢ διὰ τὴν τῶν ἄστρων φοράν·
And there is a proof of this: for the light of this circle itself is greater in one of the two semicircles, the one which has the double fold; for in this there are more and denser stars than in the other, showing that the light does not arise through any other cause than through the motion of the stars.
εἰ γὰρ ἔν τε τῷ κύκλῳ τούτῳ γίγνεται ἐν ᾧ τὰ πλεῖστα κεῖται τῶν ἄστρων, καὶ αὐτοῦ τοῦ κύκλου ἐν ᾧ μᾶλλον φαίνεται καταπεπυκνῶσθαι καὶ μεγέθει καὶ πλήθει ἀστέρων, ταύτην εἰκὸς ὑπολαβεῖν οἰκειοτάτην αἰτίαν εἶναι τοῦ πάθους.
For if it arises both in this circle in which the most stars lie, and in that part of the circle itself in which it appears to be more condensed with stars both in size and number, it is reasonable to suppose this to be the most appropriate cause of the affection.
θεωρείσθω δʼ ὅ τε κύκλος καὶ τὰ ἐν αὐτῷ ἄστρα ἐκ τῆς ὑπογραφῆς.
Let the circle and the stars in it be observed from the diagram.
τοὺς δὲ σποράδας καλουμένους οὕτω μὲν εἰς τὴν σφαῖραν οὐκ ἔσται τάξαι διὰ τὸ μηθεμίαν διὰ τέλους ἔχειν φανερὰν ἕκαστον θέσιν, εἰς δὲ τὸν οὐρανὸν ἀναβλέπουσίν ἐστι δῆλον· ἐν μόνῳ γὰρ τούτῳ τῶν κύκλων τὰ μεταξὺ πλήρη τοιούτων ἀστέρων ἐστίν, ἐν δὲ τοῖς ἄλλοις διαλείπει φανερῶς.
But those called sporadic cannot be arranged in this way on the sphere because none of them has a permanently clear position, but it is clear to those looking up at the heaven; for in this circle alone of all the circles, the spaces between are full of such stars, whereas in the others there is a manifest gap.
ὥστʼ εἴπερ καὶ περὶ τοῦ φαίνεσθαι κομήτας ἀποδεχόμεθα τὴν αἰτίαν ὡς εἰρημένην μετρίως, καὶ περὶ τοῦ γάλακτος τὸν αὐτὸν ὑποληπτέον τρόπον ἔχειν· ὃ γὰρ ἐκεῖ περὶ ἕνα ἐστὶν πάθος ἡ κόμη, τοῦτο περὶ κύκλον τινὰ συμβαίνει γίγνεσθαι τὸ αὐτό, καὶ ἔστιν τὸ γάλα, ὡς εἰπεῖν οἷον ὁριζόμενον, ἡ τοῦ μεγίστου διὰ τὴν ἔκκρισιν κύκλου κόμη.
So that if we accept the cause of the appearance of comets as having been moderately explained, we must suppose that the same holds true also for the Milky Way; for what the tail is there in relation to a single star, this same thing happens here in relation to a certain circle, and the Milky Way is, so to speak as if defining it, the tail of the greatest circle caused by the secretion.
διὸ καθάπερ πρότερον εἴπομεν, οὐ πολλοὶ οὐδὲ πολλάκις γίγνονται κομῇται, διὰ τὸ συνεχῶς ἀποκεκρίσθαι καὶ ἀποκρίνεσθαι καθʼ ἑκάστην περίοδον εἰς τοῦτον τὸν τόπον αἰεὶ τὴν τοιαύτην σύστασιν.
Therefore, as we said before, comets are not numerous nor do they appear often, because such a condensation has been and is continuously separated out at each revolution into this region.
περὶ μὲν οὖν τῶν γιγνομένων ἐν τῷ περὶ τὴν γῆν κόσμῳ τῷ συνεχεῖ ταῖς φοραῖς εἴρηται, περί τε τῆς διαδρομῆς τῶν ἄστρων καὶ τῆς ἐκπιμπραμένης φλογός, ἔτι δὲ περί τε κομητῶν καὶ τοῦ καλουμένου γάλακτος· σχεδὸν γάρ εἰσιν τοσαῦτα τὰ πάθη τὰ φαινόμενα περί τὸν τόπον τοῦτον.
So then, we have spoken of the things that arise in the world around the earth which is continuous with the motions, both of the running of stars and of the kindled flame, and moreover of comets and of the so-called Milky Way; for these are pretty much all the affections that appear in this region.