Wobbleon: Chandler Wobble
Mechanics, Chaos & Fluids arc, page 107 of 193. Back to The Pixelated Physics Universe
Who they are
Wobbleon holds up a spinning globe, and its pole drifts in a small circle he cannot quite stop.
Wobbleon is a character of the Mechanics, Chaos & Fluids arc: drawn in pixels, ruled by one piece of real physics, and never allowed to break it.
The physics
Earth's rotation axis is not fixed to the crust; the pole wanders in a loop a few metres across. In 1891 S. C. Chandler found a component with a period of about 14 months, about 433 days. A rigid Earth of the same shape would wobble freely with a period of about 305 days; the elastic mantle, the fluid core and the oceans lengthen it. The wobble damps, so something must keep exciting it. Richard Gross showed in 2000 that during 1985–1996 it was driven mainly by changes in ocean-bottom pressure, with the atmosphere second.
$$ \begin{gathered} T_{\text{Chandler}} \approx 433\ \text{days} \qquad T_{\text{rigid Earth}} \approx 305\ \text{days} \end{gathered} $$
| Symbol | Meaning | SI unit |
|---|---|---|
| $T_{\text{Chandler}}$ | observed period of the Chandler wobble (433.0 ± 1.1 d, Gross 2000) | s |
| $T_{\text{rigid Earth}}$ | free-wobble period a perfectly rigid Earth would have | s |
Honest caveat: Gross's result covers 1985–1996; the balance of excitation in other periods is still studied. The wobble is not precession, and its size in metres varies.
Sources
- Chandler (1891) On the variation of latitude, I, Astron. J. 11, 59
- Gross (2000) The excitation of the Chandler wobble, Geophys. Res. Lett. 27, 2329
Crossovers
Wobbleon meets Celtrix (Rattleback). Celtrix is a top whose spin couples to its wobble. Wobbleon's Earth isn't rigid, and its axis wanders through the crust in the Chandler wobble, with a period of about 433 days rather than the 305 days a rigid Earth would have.
Wobbleon meets Lunelock (Tidal Locking). Lunelock's tides despun the Moon. Wobbleon's Earth feels tides too, and its rotation is slowing; the Chandler wobble itself is kept going by forcing from the atmosphere and oceans.
Wobbleon meets Epochra (Precession of the Equinoxes). Wobbleon's pole wanders by metres within the crust. Epochra's axis precesses in space, about 50.3″ per year, because the Sun and Moon pull on the equatorial bulge. Different motions, both measured with care by astronomers.
Wear the lore
Concept keywords: Chandler Wobble, Wobbleon, Mechanics, Chaos & Fluids, physics lore, Pixelated Physics