The Earth is not rigid and its rotation causes it to deform, flattening at the poles and bulging at the equator. The gravitational attractions of Sun and Moon on the equatorial bulge result in torques on the Earth, which cause additional motions of the rotation axis, known as precession and nutation. These motions occur relative to a coordinate system fixed in space, for example in the solar system. The rotation axis is inclined to the pole to the ecliptic plane at a mean angle of 23.425°; this angle is the obliquity of the axis. Precession is a very slow motion of the tilted rotation axis around the pole to the ecliptic, with a period of 25,720 yr. The nutation is superposed on this motion and consists of slight fluctuations in the rate of precession as well as in the obliquity.

The other planets also affect the Earth's rotation, causing small but significant cyclical changes on a very long timescale. These are observable directly by precise measurement of the position of the rotation axis using very-long-baseline interferometry (VLBI). The fluctuations influence the intensity of solar radiation incident on the Earth and produce cyclical climatic effects that are evident in sedimentary processes, where they are known as the Milankovitch (or Milanković) cycles. They correspond to retrograde precession of the rotation axis (period ~ 26 kyr), changes in the angle of obliquity (period ~ 41 kyr), prograde precession of Earth's elliptical orbit (period ~ 100 kyr), and variation of the ellipticity of the orbit (period ~ 100 kyr).