An irregularity in the moon's orbit caused by the gravitational pull of the sun, making the moon sometimes closer and sometimes farther from Earth than expected.
From Latin 'evectio,' meaning 'a carrying away' or 'removal.' Enters English via astronomical terminology in the 17th-18th centuries. The term literally describes gravity 'carrying' the moon from its predicted path.
Ancient astronomers noticed the moon didn't follow a perfect path, but couldn't explain why until Newton's gravity—evection was one of the first proofs that invisible forces could bend the heavens in measurable ways!
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