Conventional International Origin (CIO) is a conventionally defined reference axis of the pole's average location on the Earth's surface over the year 1900.
is the movement of
Earth's
rotation axis across its surface. The axis of the
Earth's rotation
Earth's rotation or Earth's spin is the rotation of planet Earth around its own Rotation around a fixed axis, axis, as well as changes in the orientation (geometry), orientation of the rotation axis in space. Earth rotates eastward, in retrograd ...
tends, as the axis of a gyroscope, to maintain its orientation to
inertial space. The Conventional International Origin is used to measure this movement.
References
;General
* {{cite web , url=http://syrte.obspm.fr/iau/iauWGnfaTemp/Newsletter2.html , title=Newsletter 2 , work="Nomenclature for Fundamental Astronomy" (NFA) , author=Bernard Guinot , year=2003 , accessdate=2010-02-07 , publisher=
IAU
Precession