And God called the light Day, and the darkness he called Night. And the evening and the morning were the first day.
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Basil the Great
Now, henceforth, after the creation of the sun, it is day when the air is illuminated by the sun shining on the hemisphere above the earth, and night is the darkness of the earth when the sun is hidden. Yet it was not at that time according to solar motion, but it was when that first created light was diffused and again drawn in according to the measure ordained by God, that day came and night succeeded.