Res Gestae
Ammianus Marcellinus
Ammianus Marcellinus. Ammianus Marcellinus, with an English translation, Vols. I-III. Rolfe, John C., translator. Cambridge, MA; London: Harvard University Press; W. Heinemann, 1935-1940 (printing).
Now it is thought that two suns are seen, if a cloud, raised higher than common and shining brightly from its nearness to the eternal fires,[*](I.e. the sun.) reflects a second brilliant orb, as if from a very clear mirror.
Let us now turn to the moon. Then only does she suffer a clear and evident eclipse, when, rounded out with her full light and opposite the sun, she is distant from its orb by 180 degrees (i.e. is in the seventh sign).[*](Of the Zodiac.) But although this happens at every full moon, yet there is not always an eclipse.
But since the moon is situated near the movement of the earth, and is the most remote from heaven of all that celestial beauty,[*](I.e. is nearer the earth than the other heavenly bodies.) she sometimes puts herself directly under the disc[*](The sun.) that strikes upon her, and
And when under the same sign she meets the sun in a straight line, she is obscured (as was said) and her brightness is wholly dimmed; and this in Greek is called the moon’s σύνοδος.[*](Conjunction; cf. Plut., Quaest. Rom. 12, σύνοδος ἐκλειπτικὴ σελήνης πρὸς ἥλιον. That is, the time between two new moons; really, the last appearance of the waning moon, and the first of the actual new moon.)