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Chandler, Seth Carlo

variation earth’s axis period

(1846–1913) US geophysicist: discovered variation in location of the geographic poles (Chandler wobble).

By occupation both a scientist and an actuary, Chandler became interested in the possible free nutation (oscillation) of the Earth’s axis of rotation. By re-analysing repeated measurements of the latitudes of different observatories he discovered an annual variation in latitude (due to the motion of air masses) and also another variation with a period of roughly 14 months. Despite initially hostile reaction from the scientific establishment his conclusions were soon fully borne out. The cause of the secondary variation was subsequently explained and it has since become known as the Chandler wobble–the apparent motion of the Earth’s axis of rotation across the Earth’s surface (detectable as a variation of latitude with time), with a period of approximately 14 months. It is caused by the precession (or free nutation) of the Earth’s axis of symmetry about its axis of rotation. For a rigid planet the period would be exactly one year; the observed slightly longer period, and its broad spectral peak (428 ± 17 days), is due to elastic yielding of the Earth’s interior.

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