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Long-term Delta T

Monthly determinations and long-term predictions of Delta T from finals.data are provided (ASCII).  Historic Delta T and LOD are also provided (ASCII).  Terrestrial Time (TT) is defined here.

Delta T determinations

Monthly values of (TT - UT1) since 1973.  Updated quarterly.

Delta T predictions

Predictions of (TT - UT1) from the present to 2024.  Updated annually.

Historic Delta T and LOD

Provided by McCarthy and Babcock (1986).  From 1657.0 to 1984.5.

Plots of historic Delta T and historic length-of-day (LOD) are shown below.  Error bars are indicated in white.  Data points are shown in red.

deltat.png  lod.png
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