[20]
Well now, he said,
which of the proofs came after this? And I replied,
That the moon is subject to the same eclipse.
Thank you, he said,
for reminding me; but now shall I assume that you have been persuaded and do hold the moon to be eclipsed by being caught in the shadow and so turn straightway to my argument,
1
or do you prefer that I give you a lecture and demonstration in which each of the arguments is enumerated?
By heaven, said Theon,
do give these gentlemen a lecture. As for me, I want some persuasion as well, since I have only heard it put this way: when the three bodies, earth and sun and moon, get into a straight line, eclipses take place because the earth deprives the moon or the moon, on the other hand, deprives the earth of the sun, the sun being eclipsed when the moon and the moon when the earth takes the middle position of the three, the former of which cases occurs at conjunction and the latter at the middle of the month.
2
Whereupon Lucius said,
Those are roughly the main points, though, of what is said on the subject. Add thereto first, if you will, the argument from the shape of the shadow. It is a cone, as is natural when a large fire or light that is spherical circumfuses a smaller but spherical mass.
3
This is the reason why in eclipses of the moon the darkened parts are outlined against the bright in segments that are curved,
4
for whenever two round bodies come into contact the lines by which either intersects the other turn out to be circular since they have everywhere a uniform tendency.
5
Secondly, I think that you are aware that of the moon the eastward parts are first eclipsed and of the sun the westward parts and that, while the shadow of the earth moves from east to west, the sun and the moon move contrariwise towards the east.
6
This is made visible to sense-perception by the phenomena and needs no very lengthy explanations to be understood, and these phenomena confirm the cause of the eclipse. Since the sun is eclipsed by being overtaken and the moon by encountering that which produces the eclipse, it is reasonable or rather it is necessary that the sun be caught first from behind and the moon from the front, for the obstruction begins from that point which the intercepting body first assails. The sun is assailed from the west by the moon that is striving after him, and she is assailed from the east [by the earth’s shadow] that is sweeping down as it were in the opposite direction. Thirdly, moreover, consider the matter of the duration and the magnitude of lunar eclipses. If the moon is eclipsed when she is high and far from the earth, she is concealed for a little time; but, if this very thing happens to her when she is low and near the earth, she is strongly curbed and is slow to get out of the shadow, although when she is low her exertions of motion are greatest and when she is high they are least. The reason for the difference lies in the shadow, which being broadest at the base, as cones are, and gradually contracting terminates at the vertex in a sharp and fine tip. Consequently the moon, if she has met the shadow when she is low, is involved by it in its largest circles
7
and traverses its deep and darkest part; but above as it were in shallow water by reason of the fineness of the shadow she is just grazed and quickly gets clean away.
8
I pass over all that was said besides with particular reference to the phases and variations,
9
for these too, in so far as is possible,
10
admit the cause alleged; and instead I revert to the argument before us
11
which has its basis in the evidence of the senses. We see that from a shadowy place fire glows and shines forth more intensely,
12
whether because the dark air being dense does not admit its effluences and diffusions but confines and concentrates the substance in a single place or because this is an affection of our senses that as hot things appear to be hotter in comparison with cold and pleasures more intense in comparison with pains so bright things appear conspicuous when compared with dark, their appearance being intensified by contrast to the different impressions.
13
The former explanation seems to be the more plausible, for in sunlight fire of every kind not only loses its brilliance but by giving way becomes ineffective and less keen, the reason being that the heat of the sun disperses and dissipates its potency.
14
If, then, as the Stoics themselves assert,
15
the moon, being a rather turbid star, has a faint and feeble fire of her own, she ought to have none of the things happen to her that now obviously do but the very opposite; she ought to be revealed when she is hidden and hidden whenever she is now revealed, that is hidden all the rest of the time when she is bedimmed by the circumambient ether
16
but shining forth and becoming brilliantly clear at intervals of six months or again at intervals of five when she sinks under the shadow of the earth, since of 465 ecliptic full moons 404 occur in cycles of six months and the rest in cycles of five months.
17
It ought to have been at such intervals of time then that the moon is revealed resplendent in the shadow, whereas in
the shadow she is eclipsed and loses her light but regains it again as soon as she escapes the shadow
18
and is revealed often even by day, which implies that she is anything but a fiery and star-like body.
De Facie Quae in orbe Lunae Apparet. Plutarch. Harold Cherniss (Translator), William C. Helmbold (Translator). Cambridge, MA. 1957.
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