This artist's impression shows star Gliese 581, a 'Red Giant' about 20 light years away from Earth. Hypothetical 'inhabitants' of the planets orbiting this star, 581c (in the foreground), 581b and 581d (the smallest of the planets depicted here) could theoretically be about to receive signals showing the collapse of the Berlin Wall on 9 November 1989, transmitted from Earth at that time and covering the intervening distance at the speed of light.
Credit: ESO.
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