Earth orientation parameters

In geodesy and astrometry, earth orientation parameters (EOP) describe irregularities in the rotation of planet Earth. They are published by the International Earth Rotation and Reference Systems Service (IERS). EOP provide the rotational transform from the International Terrestrial Reference System (ITRS) to the International Celestial Reference System (ICRS), or vice versa, as a function of time.

Earth's rotational velocity is not constant over time. Any motion of mass in or on Earth causes a change in the rotation speed or a movement of the rotation axis. Small motions produce changes too small to be measured, but movements of very large mass, like sea currents, tides, and those resulting from earthquakes, can produce discernible changes in the rotation and can change very precise astronomical observations. Global simulations of atmosphere, ocean, and land dynamics are used to create effective angular momentum (EAM) functions that can be used to predict changes in EOP.

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