means a small, periodic drift in the earth's rotational axis relative to its crust, causing the north and south poles to trace an irregular circle a few meters wide.

from named after seth carlo chandler, an american astronomer who in 1891 discovered the wobble was real and had two overlapping cycles, not just the single one euler's math predicted in 1765 — turns out earth isn't perfectly rigid, so it wobbles a bit more sloppily than theory allowed.