HEINRICH WILHELM MATTHIAS OLBERS (1758-1840)

1823 – Germany

‘Why is the sky dark at night?’

This question puzzled astronomers for centuries and no, the answer is not because the sun is on the other side of the planet.

Olbers pointed out that if there were an infinite number of stars evenly distributed in space, the night sky should be uniformly bright. He believed that the darkness of the night sky was due to the adsorption of light by interstellar space.

This is wrong.

Heinrich-Wilhelm-Matthias-Olbers ©

OLBERS

Olbers’ question remained a paradox until 1929 when it was discovered that the galaxies are moving away from us and the universe is expanding. The distant galaxies are moving away so fast that the intensity of light we receive from them is diminished. In addition, this light is shifted towards the red end of the spectrum. These two effects significantly reduce the light we receive from distant galaxies, leaving only the nearby stars, which we see as points of light in a darkened sky.

diagram explaining reduced light intensity as the observer travels further from the source

What is light intensity?

Wikipedia-logo © (link to wikipedia)

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