Instantaneous axis of rotation


  • Webster's Revised Unabridged Dictionary
    • Instantaneous axis of rotation (Kinematics) in a body which has motions both of translation and rotation, is a line, which is supposed to be rigidly united with the body, and which for the instant is at rest. The motion of the body is for the instant simply that of rotation about the instantaneous axis.
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In science:

Universal Time (UT) defines time-of-day on Earth. There are several realizations of UT, including UTC. UT1 best represents the instantaneous orientation of Earth about its rotational axis.
The Colloquium on Decoupling Civil Timekeeping from Earth Rotation