33. Delta-T

A great deal of effort has gone into working out delta-T for the epoch of the Diaries, but no solution satisfies the precision astronomers expect.

For year 0, one recent calculation puts delta-T at 2hr 34min, another at 2hr 38min, and TheSky offers 2hr 44min. In year -400, the difference widens: a contemporary canon of eclipses estimates delta-T at 4hr 5min -- 17 minutes off from TheSky's 4hr 22min. An error of 17 minutes can affect the dating of phenomena observed near the horizon and alter the description of an eclipse.