Named after American astronomer Seth Carlo Chandler, who discovered it in the late 19th century, the Chandler wobble is a wobbling motion that occurs as the Earth spins. Scientists say it is resulting in a slow change in the Earth's axis. Much as a toy top wobbles when it slows down, the alignment of Earth's geographic poles varies as it spins.
Perhaps wobble is a bit of a misnomer, not only because it sounds like a dance, but because it may make the tiny shift sound larger than it is. The full wobble adds up to only about 20 feet (6 meters) [source: Jet Propulsion Laboratory]. Still, the effect is measurable, at least after a year. Picture a giant pen stuck through the center of the Earth, from the South Pole to the North Pole, with a scratch pad stationed directly over the North Pole. At the end of a full rotation of the Earth on its axis, the pen would have drawn a circle, not a single point. Some of the theories on the causes of the Chandler wobble are:
- the Earth's liquid interior
- constant ocean winds pushing varying amounts of water
- major earthquakes
- changing ocean pressures
- melting ice
As scientists try to determine the causes, they're faced with a sort of "chicken and egg scenario." In other words, do events such as earthquakes cause the shifts that are the Chandler wobble or does the pole shift cause changes in the Earth that lead to earthquakes? Is the answer perhaps both? Scientists do know that the massive 8.8 earthquake in Chile in 2010 affected the Earth's wobble and as a consequence affected the length of each day [source: NPR].
The wobble affects celestial navigation, because the latitude changes over a 14-month period. Although Global Positioning Systems (GPS) can mitigate the effect of the wobble on navigation systems, star charts must be updated regularly to reflect new reference points for the geographic poles. The magnetic North Pole is unaffected, so compasses still work. With the regular changes and those unexpected ones from events like major earthquakes, scientists say there are ramifications for sea level, climate and the landscape but that the revolution of our planet is intact, still spinning and wobbling a little as it always has.
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