Chandler, an actuary and amateur astronomer, published findings describing a roughly 433-day oscillation in the Earth's axis of rotation, a phenomenon distinct from precession that causes the planet's poles to trace a small, irregular circle. The discovery refined scientists' understanding of Earth's rotational dynamics and remains an active subject of geophysical research more than a century later.
Chandler was not a professional astronomer by training; he made his living as an actuary in Boston, pursuing astronomy as a devoted hobby that nonetheless yielded serious scientific contributions, including his invention of the almucantar, an instrument for precisely measuring stellar positions.
His analysis of latitude variation data revealed that the Earth's axis does not simply trace the predictable precessional wobble described by Newtonian mechanics; instead, it moves in a more complex pattern with a period of about 433 days, a free oscillation that Leonhard Euler had theoretically predicted over a century earlier but which had gone undetected.
The puzzle of why the Chandler wobble hadn't decayed away, since friction should theoretically damp it out over just a few years, persisted for decades. Modern geophysicists now believe fluctuations in ocean-bottom pressure and atmospheric circulation continually re-excite the wobble, keeping the Earth's axis in its restless, minor dance even today.
Key people: Seth Carlo Chandler