The Chandler wobble is one of several wobbling motions that Earth undergoes as it spins on its axis. It is named after Seth Carlo Chandler, Jr (1846–1913), an American businessman turned astronomer, who discovered it in 1891.

 

The Chandler wobble has a slightly variable period of 416 to 433 days and causes the location of the poles to wander by as much as 15 meters from their mean positions. Calculations show that the Chandler wobble would be damped out completely in just 68 years unless some force were constantly acting to reinvigorate it. The nature of this force remained a mystery for over a century. Various explanations were put forward involving factors such as atmospheric winds, air pressure differences, changes in lake levels, river runoff, reservoir capacities, interaction at the boundary of Earth's core, and its surrounding mantle, and earthquakes. But none of these hypotheses proved satisfactory.

 

Then, in 2001, Richard Gross, a geophysicist at the Jet Propulsion Laboratory in Pasadena, California, put the matter to rest. From computer simulations he was able to show that about two-thirds of the Chandler wobble is due to 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 remaining one third he concluded comes from fluctuations in atmospheric pressure.

 

Scientists are interested in the Chandler wobble because variations in latitude due to the wobble could throw off celestial navigation systems that are unaware of the wobble by a fifth of a mile. One such system is the program that guides US Trident nuclear missiles.

 

The Chandler wobble (CW) is also known as the Chandler period, Chandler motion, variation of latitude, and polar motion.

 

To quell rumors, there is absolutely no evidence to support the statement by pseudoscientist Lloyd Stewart Carpenter on US national radio on January 28, 2006, that the Chandler wobble has ceased with dire consequences for the planet.