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Chandler WobbleThe Chandler wobble is a small variation in Earth's axis of rotation, discovered by American astronomer Seth Carlo Chandler in 1891. It amounts to 0.7 arcseconds over a period of 435 days. In other words, Earth's poles move in an irregular circle of 3 to 15 metres in diameter, in an oscillation. The wobble's diameter has varied since discovery, reaching its most extreme range recorded to date in 1910. The cause is unknown: barring any external force, the wobble should have eventually subsided. Originally it was believed that the wobble was caused by weather fluctuations from season to season causing shifts in atmospheric mass distribution, or possible geophysical movement beneath Earth's crust. On 18 July 2000, however, the Jet Propulsion Laboratory announced that "the principal cause of the Chandler wobble is fluctuating pressure on the bottom of the ocean, caused by temperature and salinity changes and wind-driven changes in the circulation of the oceans." The Chandler wobble is a factor considered by satellite navigation systems (especially military systems). It is also theorised as the cause of major tectonic activity, including earthquakes, volcanism, El Nio, and global warming phenomenon. References Lambeck, K., 1980, The Earth's Variable Rotation: Geophysical Causes and Consequences, Cambridge University Press, London. Munk W. H. and MacDonald, G. J. F., 1960, The Rotation of the Earth, Cambridge University Press, London. External links *Jet Propulsion Laboratory press release announcing cause of the Chandler wobble
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