Plutarch, De facie quae in orbe lunae apparet
Harold Cherniss and William C. Helmbold, Ed.

With these remarks I was about to yield the floor to Lucius,¹ since the proofs of our position were next in order; but Aristotle smiled and said: ‘The company is my witness that you have directed your entire refutation against those who suppose that the moon is for her part semi-igneous and yet assert of all bodies in common that of themselves they incline either upwards or downwards. Whether there is anyone, however, who says² that the stars move naturally in a circle and are of a substance far superior to the four substances here³ did not even accidentally come to your notice, so that I at any rate have been spared trouble.’ And Lucius <broke in and> said: ‘. . . good friend, probably one would not for the moment quarrel with you and your friends, despite the countless difficulties involved, when you ascribe to the other stars and the whole heaven a nature pure and undefiled and free from qualitative change and moving in a circle whereby <it is possible to have the nature> of endless revolution too; but let this doctrine descend and touch the moon, and in her it no longer preserves the impassivity and beauty of that body. Not to mention her other irregularities and divergencies, this very face which she displays is the result of some alteration of her substance or of the admixture somehow of another substance.⁴ That which is subjected to mixture, however, is the subject of some affection too, for it loses its purity, since it is perforce infected by what is inferior to it. The moon's sluggishness and slackness of speed and the feebleness and faintness of her heat <which>, in the words of Ion,

ripes not the grape to duskiness,⁵

to what shall we ascribe them except to her weakness and alteration, <if> an eternal and celestial⁶ body can have any part in <alteration>? The fact is in brief, my dear Aristotle, that regarded as earth the moon has the aspect of a very beautiful, august, and elegant object; but as a star or luminary or a divine and heavenly body she is, I am afraid, misshapen, ugly, and a disgrace to the noble title, if it is true that of all the host in heaven she alone goes about in need of alien light,⁷ as Parmenides says ‘Fixing her glance forever on the sun.⁸ ’ Our comrade in his discourse⁹ won approval by his demonstration of this very proposition of Anaxagorass that ‘the sun imparts to the moon her brilliance’ ¹⁰; for my part, I shall not speak about these matters that I learned from you or in your company but shall gladly proceed to what remains. Well then, it is plausible that the moon is illuminated not by the suns irradiating and shining through her in the manner of glass¹¹ or ice¹² nor again as the result of some sort of concentration of brilliance or aggregation of rays, the light increasing as in the case of torches.¹³ Were that true, we should see the moon at the full on the first of the month no less than in the middle of the month, if she does not conceal and obstruct the sun but because of her subtility lets his light through or as a result of combining with it flashes forth and joins in kindling the light in herself.¹⁴ Certainly her deviations or aversions¹⁵ cannot be alleged as the cause of her invisibility when she is in conjunction, as they are when she is at the half and gibbous or crescent; then, rather, ‘standing in a straight line with her illuminant’, says Democritus, ‘she sustains and receives the sun,’ ¹⁶ so that it would be reasonable for her to be visible and to let him shine through. Far from doing this, however, she is at that time invisible herself and often has concealed and obliterated him.

His beams she put to flight,

as Empedocles says,

From heaven above as far as to the earth,
Whereof such breadth as had the bright-eyed moon
She cast in shade,¹⁷

just as if the light had fallen into night and darkness and not upon 〈an〉 other star. As for the explanation of Posidonius that the profundity of the moon prevents the light of the sun from passing through her to us,¹⁸ this is obviously refuted by the fact that the air, though it is boundless and has many times the profundity of the moon, is in its entirety illuminated and filled with sunshine by the rays. There remains then the theory of Empedocles that the moonlight which we see comes from the moons reflection of the sun. That is why there, is neither warmth¹⁹ nor brilliance in it when it reaches us, as we should expect there to be if there had been a kindling or mixture of <the> lights <of sun and moon>.²⁰ To the contrary, just as voices when they are reflected produce an echo which is fainter than the original sound and the impact of missiles after a ricochet is weaker,

Thus, having struck the moon's broad disk, the ray²¹

comes to us in a refluence weak and faint because the deflection slackens its force.’