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The 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 433 days. In other words, Earth's poles move in an irregular circle of 3 to 15 metres in diameter, in an oscillation. This is in addition to the precession of the equinoxes, a larger oscillation which takes over 25,000 years to complete.

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 seasonal weather fluctuations 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."^[1]

The Chandler wobble is a factor considered by satellite navigation systems (especially military systems). It is also claimed to be the cause of major tectonic activity, including earthquakes, volcanism, El Niño, and global warming phenomenon, however there is no actual data which supports such a claim.

During the first hour of the national radio broadcast of Coast to Coast AM on January 28, 2006, Lloyd Stewart Carpenter reported that the Chandler wobble had stopped (i.e. its amplitude had reduced to zero) and that it could be a harbinger of a catastrophic pole shift. In fact there was a near six week period in which a significant pause occurred. This was first noted by the International Earth Rotation Service on or about January 5, 2006 as the path of the wobble, usually a widening or tightening spiral depending on the depth of the cycle, made a 90° departure from its predicted track. It proceeded to cease any substantial movement until on or about February 11th when the wobble appeared to begin tracing a path back toward its normal route. This anomaly has been of great interest in gaining a better understanding, but it is not yet known if this has or will cause any catastrophic changes in the overall rotation axis of the planet.

The Chandler wobble changes over time, with U.S. Navy data over the past several years showing the wobble has diminished as of mid-late 2005. However, this is likely transient, as the wobble has increased and decreased many times in the past and will likely do so a great many more times in the future.

• Polar motion

http://www.jpl.nasa.gov/releases/2000/chandlerwobble.html

please consider the chandler wobble solved since 2000 as stated here by scientists at the jpl nasa.

1. ^ A Mystery of Earth's Wobble Solved, Jet Propulsion Laboratory press release announcing cause of the Chandler wobble, July 18, 2000

• Carter, B, and M.S, Carter, 2003, "Latitude, How American Astronomers Solved the Mystery of Variation", Naval Institute Press, Annapolis.
• 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.

• International Earth Rotation Service (IERS) incorporating the Earth Orientation Paramaters (EOP) and International Celestial Reference System (ICRS) groups
• The United States Naval Observatory - graph for 2005 and historical data
• Mystery of wobbly Earth solved, July 19, 2000
• Major Anomaly In Chandler's Wobble, Michael Mandeville