But although the moon sometimes hides all the sun, yet that eclipse continues not so long nor is so far extended, but there always appears about the circumference a certain brightness, which permits not the darkness to be black, deep, and perfectly obscure. And Aristotle (I mean the ancient philosopher of that name) rendering the reason why there are oftener seen to happen eclipses of the moon than of the sun, among other causes alleges this, that the sun is eclipsed by the interposition of the moon, and the moon by that of the earth, which is much greater and consequently oftener opposes itself. And Posidonius thus defines this accident: The eclipse of the sun is the conjunction of the sun and moon, the shadow of which darkens our sight.[98] For there is no eclipse except to those whose sight the shadow of the moon intercepting hinders them from seeing the sun. Now in confessing that the shadow of the moon descends down to us, I know not what he has left himself to say. It is certainly impossible for a star to cast a shadow; for that which is not enlightened is called a shadow, and light makes no shadow, but on the contrary drives it away. 20. But what arguments, said he, were alleged after this? The moon, answered I then, suffered the same eclipse. You have done well, replied he, to put me in mind of it. But would you have me go on and prosecute the rest of the discourse, as if you had already supposed and granted that the moon is eclipsed, being intercepted within the shadow of the earth? Or shall I take for the subject of a declamation the making a demonstration of it, by rehearsing to you all the arguments, one after another? Nay, by Jove, said Theon, let this be the argument of your discourse. For I indeed stand in need of some persuasion, having only heard that when these three bodies, the earth, the moon, and the sun, are in a direct line, then eclipses happen; for that either the earth takes the sun from the moon, or the moon takes him from the earth. For the sun suffers an eclipse when the moon, and the moon when the earth, is in the midst of the three; of which the one happens in the conjunction or new moon, and the other in the opposition or when the moon is full.