Video – Why is the Sky dark at night? (The Olbers Paradox)
From common sense it is normal for the sky to be dark at night, but if it is true that the universe has an infinite number of stars – if we think about it – it shouldn’t to be so. With an infinite number of stars, each element of the sky background should have a star – more or less distant – and the entire sky should be at least as bright as an average star like the Sun.
The fact that the night sky is not as bright as the sun is called the Olbers paradox. It can be traced back to Kepler in 1610, and was re-discussed by Halley and Cheseaux in the eighteenth century, but it wasn’t popularized as a paradox until Olbers (a German physician and amateur astronomer) addressed the issue in the nineteenth century.
Possible explanations that have been given over the years
There are many possible explanations that have been considered. Here are some of them:
– There is too much interstellar dust to see distant stars, which remain hidden from it.
– The universe has only a finite number of stars.
– The distribution of the stars is not uniform. So, for example, there could be an infinity of stars, but they are hiding one after the other.
– The universe is expanding, so the light from distant stars is redshifted, and therefore invisible.
– The universe is young. The distant light has not yet reached us.
– The light of some stars will never reach us, and therefore we will never be able to see them.
Some of these explanations are completely wrong. What will be the correct motivation? Or the correct reasons, if there is more than one?
Here is the video explaining the Olbers paradox, enjoy!
And here is a selection of some great astronomy books that are not only instructive to read, but also fun.