Table A gives the value of AT for the beginning of some years. Except for the two last values, they are taken from the Astronomical Almanac for 1988 (Washington, D.C.), pages K8 and K9. For epochs before the year 1620 or in the future, an approximate value of AT, in seconds, can be deduced from the following relation due to Morrison and Stephenson:

This leads to Table B. It should be noted that for the very past and future, the tabulated values of AT may be in error by many minutes, as the fluctuations due to the variable rotation of the Earth are unknown for those remote epochs.

Tabulated times in TD may be converted into Universal Time by subtracting from them the quantity AT, since we have UT = TD - AT.

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