Alcuin of York — on Rev 8:12 (COMMENTARY ON REVELATION)

“And the fourth angel sounded the trumpet, and the third part of the sun was smitten, and the third part of the moon, and the third part of the stars, so that the third part of them was darkened, and the day did not shine for a third part of it, and the night in like manner. By the sun, the moon, and the stars is symbolized the Church, and their darkness refers particularly to the perfidy of the heretics. Although two parts are made out of three thirds, namely one part belonging to the day with the sun, and another belonging to the night with the moon and the stars, the two nonetheless make one, or one is subdivided into two. He does this in order to indicate its overt error by the day, and its hidden error by the night, that is, respectively, the public conflicts of the heretics and their secret machinations. The reason why it is not said "the third part was smitten and darkened" but the third part was smitten so that it might be darkened (in due time), is that it is when they are openly separated from the Church that the heretics are truly darkened; for before that they are, as it were, hiddenly wounded. They are smitten out of the light of faith and the brightness of the divine Word. This destruction should not be ascribed to God, but understood in the same way as Pharaoh's heart being hardened. [Ex. 4:21; 7:3, 13, 22; 8:19; 9:12, 35; 10:1, 20, 27; 11:10; 14:4, 8]”