in IERS Bulletin A is published earth orientation data about the past ("Rapid Service" computed once a week and "Final Values" computed once a month) and predictions for the future.
compute the difference between predicted versus actual. when have predictions been wrong? what caused the incorrect predictions? we guess weather (atmospheric angular momentum) and earthquakes. what are their relative contributions to error? what else? maybe the movements of mantle and core deep inside the earth are significant and unpredictable week to week.
DUT = UT1 - UTC is one parameter of earth orientation, easy to understand: how much has the earth actually turned relative to our clocks?
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