For more than a century astronomers have known that the earth wobbles on its axis as it journeys through space. A number of credible theories have been advanced as to just why this might be so. Now, it seems, we know. Global positioning system (GPS) technologies now allow us to measure the earth’s wobble within a few millimeters over the course of the last decade, and have enabled scientists at universities in the United States and England and the Jet Propulsion Laboratories to prove the validity of one explanation.

The scientists have determined that when large amounts of surface matter on the earth shift—for example, when glaciers and ice sheets melt in the spring, or when they freeze in the winter—it “throws the earth off balance.” The wobble occurs because the poles adjust to compensate.

The earth, of course, isn’t a sphere, but an ever-so-slightly-tetrahedronic oblate spheroid, with a pronounced bulge at the equator that’s created by the force of the earth’s rotation. Even a shift of a few millimeters in the position or height of the bulge can be measured using GPS. What the scientists learned, and document, is that changes in shape are directly correlated with the wobble, proving their theory.
(Geophysical Research Letters)

–From the May 2004 Austin Review KB