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The image is derived from two astronomers who have spent considerable time considering time. In 1992 Seidelmann and Fukushima published an explanation of why the IAU had introduced even more new time scales in 1991 after they had already introduced new time scales in 1976. The following is Figure 1 from that paper.

plots of deltas between time scales

The figure shows the differences between the different time-like arguments and time scales between 1950 and 2020. The periodic terms of TCB and TDB are magnified by 100 to make them visible. TAI us used as the reference, and ET, TDT, and TT are all taken as (TAI + 32.184 s).

Steve Allen <>
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