Conventional International Origin

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.[1]

Polar motion is the movement of Earth's rotation axis across its surface. The axis of the Earth's rotation tends, as the axis of a gyroscope, to maintain its orientation to inertial space. The Conventional International Origin is used to measure this movement.


  • Bernard Guinot (2003). "Newsletter 2". "Nomenclature for Fundamental Astronomy" (NFA). IAU. Retrieved 2010-02-07.
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