Reading Milton's universe

The universe is a vast sphere of everlasting daylight, and night, as experienced on earth, is merely a shadow cast by the planet with the sun behind it: ‘the circling canopy’, as John Milton put it, ‘Of night’s extended shade’, beyond which there are only ‘happy climes that lie / Where day never shuts his eye’.

Mounting evidence suggests that Milton was not an exception: that although not universal, bright space belief was common in European premodernity, and that widespread acceptance of dark space is a much more recent phenomenon than we might think. When did space turn dark, and what is the significance of this question for modern readers of Paradise Lost?