Sun and moon as signs and the nature of night

Think of the sun in the same way, with one difference: the sun received the light once and holds it blended with itself, and never puts it off. The moon, by contrast, is continually stripping off the light, so to speak, and putting it on again, and by its own behavior it confirms what has been said about the sun. These lights were also appointed to separate between the day and between the night. For above, God separated between the light and between the darkness; then he set their natures in opposition to each other, so that they have no mixing with one another, and light has nothing in common with darkness. What a shadow is in the daytime, that is what we should understand the nature of darkness to be at night. For every shadow falls from bodies that block a shining ray, lying opposite the light; in the morning it stretches toward the west, in the evening it leans toward the east, and at noon it lies to the north. So too the night withdraws in the direction opposite the sun's rays, being nothing other in its nature than a shadowing of the earth. Just as in the daytime a shadow comes into being from whatever blocks the light, so the night naturally comes into being when the air around the earth is cast into shadow. This, then, is what is meant by the words, God separated between the light and between the darkness: the darkness flees the assaults of the light, because at the first creation their estrangement from one another was built into their natures. But now he commanded the sun to govern the measures of the day, and the moon, whenever it completes its own cycle, he made the ruler of the night. For at that time the lights stand nearly opposite one another across the diameter. When the sun rises at the full moon, the moon sinks down out of sight; and when the sun sets again, the moon often rises opposite it from the east. If in its other phases the moon's light does not exactly coincide with the night, that has no bearing on the present discussion. The point is that when the moon is at its fullest, it begins the night, outshining the stars with its own light and illuminating the earth, and it divides the measures of time equally with the sun. "And let them be for signs, and for seasons, and for days, and for years" (Genesis 1:14). The indications given by the lights are necessary for human life. If one does not busy himself beyond measure with the signs they give, he will find their observations, gained from long experience, useful. From them one can learn many things about heavy rain, and many things about droughts and the movement of winds, whether local or general, violent or gentle. One of the signs drawn from the sun the Lord himself has handed on to us, when he said, "There will be a storm, for the sky reddens, being gloomy" (Matthew 16:3). For when the sun rises through mist, its rays are dimmed, and its color appears like coals and tinged with blood, because the thickness of the air produces this appearance to the eyes. The air, which until then was dense and compact and not dispersed by the ray, shows that it could not be overcome because of the influx of vapors from the earth, but by the excess of moisture it will bring a storm upon the regions where it gathers.