# How to measure the cycles of earth moving/rotation?

My knowledge of science is very basic, but after some research I have some knowledge, but I am still not clear with so many things regarding to this earth.

I have read Laser's Measure the Earth's Rotation and Wobble but would appreciate it if anyone who knows science well, could explain how the rotation of the Earth is measured and how it is affected by the Chandler wobble and the annual wobble?

• What do you mean by "measure the cycles of earth moving"? I think we have a language understanding problem. – gerrit Mar 3 '15 at 5:26
• Hi both sorry for poor with English writing :), what I mean is cycle of earth roll or rotation. here is what I mean livescience.com/17619-lasers-measure-earth-rotation-wobble.html But I don't know what is the measurement to proof. – pitoukhmer Mar 3 '15 at 6:22
• Thank @Fred for your correcting me, that really appreciated – pitoukhmer Mar 3 '15 at 7:04

In theory, if the Earth was a solid object, the Chandler wobble would be easy to understand. It's simply a result of the polhode rolling without slipping on the herpolhode lying in the invariable plane. In other words, $\mathrm I \dot \omega + \omega \times (\mathrm I \omega) = 0$, where $\mathrm I$ is the Earth's inertia tensor and $\omega$ is the Earth's angular velocity. The Chandler wobble is simply the consequence of the Earth not having a spherical mass distribution and the Earth not having it's angular momentum and angular velocity coaligned.