• The canals of Mars were first described (as Canali, channels, originally without implying artificiality) by Giovanni Schiaparelli in 1877. They later became a cause celebre because they were taken up, mainly by US astronomer Percival Lowell, as a sign of life – and indeed large-scale civil engineering – on the surface of Mars. It turns out that they are optical illusions based on the tendency of the eye to make order out of random blotchy patterns like those seen on the surface of Mars. The laws of optics dictate that the canals as drawn by their supporters like Lowell were beyond the resolving power of the telescopes used.

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