We show that the leap second is due to time scale divergence between Universal Time (UT) and International Atomic Time (TAI) because the System Internationale (SI) second is shorter than the UT second. This is demonstrated by a thorough analysis of the procedures that were followed to produce Ephemeris Time (ET) to which the SI second was calibrated. This paper shows that time dilation is responsible for the ET second being shorter than the UT second. Over the past century, it was well documented that observed lunar and planetary positions always lagged behind calculated positions. ET was introduced to remove this discrepancy. Deceleration of Earth's rotation contributed less than 1% of this time scale divergence, according to paleontological records of tidal fraction. Our calculation of the time dilation effect match the difference between the SI and UT seconds and also match the leap second insertion rate to within 0.2% since atomic time began in 1958. A method to convert from the TAI time scale using a scalar to obtain a precise UT time scale is given with leap seconds needed only once every 14 decades due to tidal friction.