## By how much does the axis of the Earth shift when it wobbles?

There is a component to the total wobble called the Chandler Wobble which has roughly a period of 14 months, and an amplitude of +/- 0.7 seconds of arc. The figure above shows the path traced out on the surface of the Earth by its instantaneous rotation axis from 2001 through 2005.You can see that after a little more than a year, the polar position has returned within a few meters of its starting point. The dither causes the North and South Poles to execute roughly a circular path about the nominal polar directions, with a circle whose radius is about 0.7 seconds of arc. If you were standing at the mean geometric north pole, the Chandler Wobble would carry the actual pole on a circle about 5 meters in radius, and at a speed of about 2 x pi x 5/14 months = 2 meters/month or 2 inches per day around this circular path. No two Chandler Wobbles are exactly the same and the 'orbits' change in radius from cycle to cycle so the polar wander 'orbit' does not rejoin itself. This is probably due to viscous damping inside the Earth, or the movement of mass near the surface (clouds, water etc).

Superimposed on this are higher-frequency, daily disturbances at the milli-arc second level that are due to the motion of air masses, weather systems and other 'diurnal' influences.