IF YOU’RE planning a spot of polar exploration, here’s something you might want to consider. When, after that arduous trek across the ice sheet, you pose at the pole for a snapshot, you might be standing in the wrong place. In fact, the pole could be up to 10 metres from where it was only six months before.
Implausible as it sounds, the Earth’s surface is constantly shifting relative to its axis so that the geographical poles wander all over the place. It may only be a few metres a year, and it’s certainly not noticeable from day to day, but this polar wobble has been enough to puzzle stargazers for more than 100 years.
To add to the confusion, there are actually three types of wobble. Two of them were discovered and measured in the 19th century, though only explained in the last decade: the Chandler wobble takes 14 months to complete a cycle, while the annual wobble, as the name suggests, takes exactly a year. Both are driven largely by weather and ocean currents (see “Seasonal swings”).
In 1960, William Markowitz of the US Naval Observatory in Washington DC noticed what appeared to be another, subtler form of polar wander, which moved the poles by about a metre on what seemed to be a 24-year cycle. Nobody could explain it.
Now a young geologist at the UK’s University of Leeds says he has found an explanation for the Markowitz wobble. If he’s right, studying the wobble could reveal some of the secrets of the most mysterious part of the Earth – its inscrutable inner core.
The first clear …
