... defined the second to be the time ittakes the cesium 133 atom to make exactly 9, 192 ,631,770 transitions. The choiceof 9, 192 ,631,770 was made to make the atomic second equal to the mean solar second ... ticks of the cesium 133 clocks sincemidnight on Jan. 1, 195 8 (the beginning of time) divided by 9, 192 ,631,770.Although TAl is highly stable and available to anyone who wants to go to thetrouble ... anything to do with papal decrees and did notaccept the Gregorian calendar for 170 years.Figure 6-3. TAl seconds are of constant length, unlike solar seconds. Leapseconds are introduced when necessary...