why is the sky dark at night
The sky is dark at night… …yes, I can hear you saying, I’ve noticed. But actually the reason why the sky is dark at night is not as obvious as it might seem – and is certainly not just because the sun is ‘round the other side of the Earth’. ... The problem is this: if the universe contains enough stars, then they should appear to overlap each other in the sky like tree trunks in the middle of a forest. The whole sky would be as bright as the surface of the Sun, whether by night or by day. ... But besides being very hard to imagine, the trouble with an infinite Universe is that astronomers soon calculated that it did indeed mean that stars should be overlapping like tree trunks – and the night sky would then be blazing with light. ... The sky would not just be bright, it would be infinitely bright! ... So the question of why the sky is dark at night is really quite difficult – and gradually made people think that they might be wrong in assuming that the universe had no beginning, no end, and is the same everywhere. ... It is this time limit that makes the sky dark at night, because only light from the stars that are close enough to us has had time to reach here, and they are not enough to ‘light up the sky’.