The Byzantines, in their Suda encyclopedia/lexicon of the 10th Century, wrote this about eclipses:

Under entry Ἔκλειψις (eclipse), it reads:

The eclipse of the sun, when it is being obscured by the moon, appears to take place distinctly.

Furthermore, under a linked entry (transparent), they write:

They say that something transparent is a nature present in many substances that lets things pass through. When light is not present this thing itself is transparent in potentiality, but becomes transparent in actuality when light is present. Not only are the air and water transparent, but also many of the solid materials, such as moonstones, horns, glass, gypsum, and other things. The celestial material also partakes of transparency and invisibility, such as the fluid of the spheres; for it is completely transparent. Indeed, we see the stars in the firmament through it. Now the spheres are transparent but the stars are not transparent at all, and this is why they get in each others' way. Hence eclipses of the sun, at least, clearly appear to happen when the moon gets in its way.

In many other works from Byzantium, it is shown that the Byzantines were well aware of the mechanics of astronomical processes. In Anna Komnene's Alexiad, she remarks on a trick pulled by her father, Emperor Alexios I Komnenos, to outwit the invading Pechenegs (called 'Scythians') with science:

In the course of the discussion a certain Nicholas, one of the Emperor's secretaries, came up to him and whispered in his ear, "You may expect an eclipse of the sun to take place today", and on the Emperor's expressing a doubt, he swore with an oath that he was not lying. Then the Emperor, with his habitual quick-wittedness, turned to the Scythians and said, "I appoint God as judge; and if a sign appears in the heavens this day, you will know for a surety that I have good reason for suspecting, and therefore not receiving, your embassy because your leaders are not sincere in their overtures for peace. If, however, no sign appears, I shall stand convicted of having been wrong in my surmise." Before two hours had passed, the light of the sun failed, and the whole of its disc was darkened by the moon's passing over it. At that sight the Scythians were terrified, and the Emperor handed them over to Leo Nikerites (he was a eunuch, brought up among the soldiers from babyhood, and much respected) and ordered him to take a sufficient guard and conduct them to the Queen of Cities.