What Is the Chandler Wobble?

The Chandler wobble is the change in the spin of Earth on its axis. photovideostock / Getty Images

The Chandler wobble is the change in the spin of Earth on its axis. Think of the wobble you see in a toy top when it first starts spinning or slows down. Its "poles" do not spin in a perfectly straight line.

The displacement of the Chandler wobble is measurable -- Imagine a gigantic ballpoint pen poked through the center of the earth, entering at the South Pole and exiting at the North Pole. Imagine the pen is drawing on a scratch pad-equipped space station directly over the North Pole. After a day (one full rotation of the earth on its axis) the ballpoint pen draws a circular path, and not a dot, because of the "wobble" in the earth's rotation on its axis. (A Doodletop, a toy drawing tool that is a pen attached to a top, draws the same sort of path.) Over 14 months the pen draws a spiral path similar to this drawing.

The American astronomer Seth Carlo Chandler discovered the wobble in the late 1800s. The exact cause of the wobble in Earth's polar motion has stumped scientists with few agreeing on the actual cause, other than the fact that the planet is not a perfect sphere.

There are theories about the cause and the effect of the wobble. Some think tides and the liquid interior of the earth could play a part. As others have reported recently, some clues have been discovered. Some of the more recent conjectures include the constant winds over the oceans pushing varying amounts of water on the earth at one time or even the effects of a major earthquake. This article talks about one of the most recent theories, which attributes most of the wobble to pressure changes in the ocean.

The chandler wobble doesn't really have any effect on most people. The people who live with it on a daily basis are astronomers using earth-based telescopes and people using various navigation systems. With telescopes, the wobble affects the ability to point at a star accurately. The Chandler wobble also affects celestial navigation, since the latitude does change over a period of 14 months. Global Positioning Systems, (GPS), can overcome the effect of the wobble on navigation. Navigators' star charts, however, still have to be updated to show the new reference point for the geographic North and South Poles. The magnetic North Pole, used by a compass, is not affected.

Here are some interesting links:

Chandler Wobble FAQ

What causes the Chandler wobble?

The "wobble" is caused by pressure changes on the seabed and atmospheric pressure fluctuations.

What is the period of the Chandler wobble?

The Chandler wobble has a period of 433 days.

What is the wobble of Earth's axis called?

The wobble of Earth's axis is known as "Axial Precession" or "Precession of the Equinoxes."

When was the last time the Earth's axis shifted?

The Earth's axis is always shifting very slowly, but one of the most significant recent shifts was detected in the 20th century. The rapid melting of glaciers due to climate change has been causing the North Pole to shift in an eastward direction since 2000.

What are the effects of the Chandler wobble?

The Chandler wobble doesn't have significant direct effects on our everyday lives, but it does slightly affect the precise coordinates of places on Earth and anything that depends on them, such as GPS, Earth-observing satellites, and astronomical observations.