Editing Polar motion (section)

{{About|motion relative to the crust|motion relative to an astronomical framework|axial precession|and|astronomical nutation}}
{{Short description|Motion of Earth's rotational axis relative to its crust}}
[[File:PolarMotion.png|thumb|upright=1.5|Polar motion in [[arc-seconds]] as function of time in days (0.1 arcsec ≈ 3 meters).<ref>{{cite journal|first1=M. |last1=Folgueira |journal=Astron. Astrophys.|year=2005 |bibcode=2005A&A...432.1101F |title=Free polar motion of a triaxial and elastic body in Hamiltonian formalism: Application to the Earth and Mars|volume=432|issue=3|pages=1101–1113|doi=10.1051/0004-6361:20041312|url=https://digital.csic.es/bitstream/10261/25910/1/articulo4_2005.pdf|doi-access=free}}</ref>]]

'''Polar motion''' of the Earth is the motion of the [[Earth's rotation|Earth's rotational axis]] relative to its [[Earth's crust|crust]].<ref name=Lambeck>{{cite book|last1=Lambeck|first1=Kurt|title=The earth's variable rotation : geophysical causes and consequences|date=2005|publisher=Cambridge University Press|location=Cambridge|isbn=978-0521673303|edition=Digitally printed}}</ref>{{rp|1}} This is measured with respect to a reference frame in which the solid Earth is fixed (a so-called ''Earth-centered, Earth-fixed'' or [[ECEF]] reference frame). This variation is a few meters on the surface of the Earth.