THE MEAN-SOLAR-TIME ORIGIN OF UNIVERSAL TIME AND UTC

摘要

Universal Time is the measure of Earth rotation that serves as the astronomicalbasis of civil timekeeping. Since the end of the 19th century, Universal Timehas been maintained to preserve continuity with Newcomb's mean solar timeat Greenwich. Here, the concept of a fictitious mean sun is revisited and comparedwith UT1. Simulations affirm that Universal Time has separated fromNewcomb's mean sun by approximately (1/365) △T as predicted by theory.The disparity is about 0.2~s presently, which is much less than the ±0.9~s differencesallowed between UT1 and UTC, the atomic realization of mean solartime used for civil timekeeping.