Olbers' Paradox

 The rain has finally stopped and the sky is clearing. I've just been outside and taken the above photograph of the stars shown on my planisphere below. So why is the sky so black?

Olbers was an 18th Century German astronomer who first hit on the idea that if the Universe was infinitely big and had existed for an infinite length of time, the sky at night should be white. That's because there would by logic be a star in every direction, given even distribution through space. In the infinite time available, light from every direction would have time to reach us. He concluded that the Universe was therefore finite. I had always taken that to mean that it had a limited size, but the stuff I read now seems to suggest that the Universe is infinite in size. But it is finite in TIME. So they now talk about the OBSERVABLE UNIVERSE, the bit from which light has had time to reach us.