Geophysics Earth rotation and tides Fact

Chandler wobble

Builds on Polar motion Euler free nutation

Statement

The polar motion of the Earth contains a free oscillation, the Chandler wobble, with a period of about $433$ days. In it the rotation pole moves around its mean position, counterclockwise as seen from above the North Pole. This period is longer than the Euler period of about $305$ days. The Euler period is the period of the Euler free nutation of a rigid Earth with the same moments of inertia.

Remarks

For a rigid axisymmetric body, Euler's equations give a free wobble with period $A/(C-A)$ rotation periods, where $A < C$ are the principal moments of inertia. For the Earth this is about $305$ days. The Earth is not rigid: the elastic yielding of the mantle, the oceans and the fluid core reduce the effective restoring effect of the equatorial bulge, which lengthens the period. The wobble would decay by friction, so it must be excited continually; fluctuations of pressure in the atmosphere and the oceans are thought to be the main source. It was discovered by the astronomer Seth Carlo Chandler in 1891 from variations of the latitudes of observatories. Its amplitude varies over decades, and on the Earth's surface it is a motion of a few metres.

Going deeper

For a student

The Chandler period is a measurement of the Earth's response to slow changes of its centrifugal potential. It depends on the Love numbers, in particular on $k_2$ , and on the ocean and core, so it is a test of models of the Earth's interior. The other large part of polar motion is an annual oscillation forced by seasonal shifts of air and water. The sum of the two shows a beat of about six years.

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Tag	`9RESF83PY2`
URI	`m2://9RESF83PY2`
Kind	statement, fact
Writing	W0 stub
MSC	86A30, 70E15
Status	This copy of the site has no build data. Run `m2 status 9RESF83PY2`.
About	Polar motion
Uses	Polar motion, Euler free nutation
Changed	3 November 2026