What is the Chandler Wobble?

The Chandler wobble involves a shift in Earth's rotation. Imagine the wobble of a spinning top as it begins or slows down. The Earth's poles don't spin in a perfectly straight line.

The movement of the Chandler wobble can be measured. Picture a giant ballpoint pen piercing through the Earth's center at the South Pole and exiting at the North Pole. This pen would draw on a scratch pad-equipped space station directly above the North Pole. After one full rotation of Earth, the pen traces a circular path, not a single point, due to the wobble in Earth's rotation. (A Doodletop, a toy with a pen attached to a spinning top, creates a similar pattern.) Over 14 months, this path turns into a spiral like this drawing.

In the late 1800s, American astronomer Seth Carlo Chandler identified the wobble. The precise cause of the Earth's polar motion remains uncertain, with few scientists agreeing on its origin, aside from the fact that Earth is not a perfect sphere.

There are various theories regarding the cause and impact of the wobble. Some suggest that tides and the Earth's liquid interior may play a role. As recent studies have pointed out, new clues have emerged. Among the latest speculations are the effects of consistent winds across the oceans, pushing different amounts of water on the earth at different times, or even the influence of a significant earthquake. This article discusses one of the newest theories, which links most of the wobble to pressure variations in the ocean.

The Chandler wobble doesn’t have much of an effect on the general public. However, those who experience it daily include astronomers with ground-based telescopes and people using various navigation systems. For astronomers, the wobble interferes with precise star alignment. It also impacts celestial navigation, as the Earth's latitude shifts over a 14-month cycle. Global Positioning Systems (GPS) can compensate for the wobble's influence on navigation. However, navigators still need to update their star charts to reflect the new reference points for the geographic North and South Poles. The magnetic North Pole, used by compasses, remains unaffected.

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