Why Is The Earth Moving Away From The Sun?

Photo: The sun and Earth are moving apart by about 15 cm per year - the culprit may be tides raised on the sun by our home planet (Image: NASA)

From New Scientist:

Skywatchers have been trying to gauge the sun-Earth distance for thousands of years. In the third century BC, Aristarchus of Samos, notable as the first to argue for a heliocentric solar system, estimated the sun to be 20 times farther away than the moon. It wasn't his best work, as the real factor is more like 400.

By the late 20th century, astronomers had a much better grip on this fundamental cosmic metric – what came to be called the astronomical unit. In fact, thanks to radar beams pinging off various solar-system bodies and to tracking of interplanetary spacecraft, the sun-Earth distance has been pegged with remarkable accuracy. The current value stands at 149,597,870.696 kilometres.

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