Читать книгу Global Navigation Satellite Systems, Inertial Navigation, and Integration - Mohinder S. Grewal - Страница 64

Coordinated universal time (UTC) is the timescale based on the atomic second but is occasionally corrected by the insertion of leap seconds so as to keep it approximately synchronized with the Earth's rotation. The leap second adjustments keep UTC within 0.9 seconds of UT1, which is a timescale based on the Earth's axial spin. UT1 is a measure of the true angular orientation of the Earth in space. Because the Earth does not spin at exactly a constant rate, UT1 is not a uniform timescale [5].