Over the next several hundred million years, Earth could face numerous unexpected consequences, all due to the distance slowly yet steadily developing between the planet and its only moon. In what is coming to be defined as one of the most precisely known physical quantities in all of contemporary planetary science, the Moon is moving away from Earth at the speed of 3.83 centimetres annually, with a formal uncertainty of approximately 0.09 millimetres.The number is based on the current best interpretation of five decades of lunar laser ranging data. It has been directly measured, thousands of times over, from multiple observatories on three continents, by firing laser pulses at retroreflector arrays that Apollo astronauts left on the lunar surface between 1969 and 1971.On the human timescale, the rate is roughly the rate at which human fingernails grow. Over a human lifetime, it accumulates to approximately three metres. Over the span of recorded human civilisation, roughly five thousand years, it accumulates to approximately 190 metres. On these timescales, the Moon is, for all practical purposes, sitting where it has always sat. But on geological timescales, the picture is substa...







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