This table gives mean annual values of the duration of the day (its excess
D to 86400 s), which are available for the last four centuries. For the
interval 1623-1955, the data are those provided by L.V. Morrison, Royal
Greenwich Observatory, interpolated for the middle of the year. The mean
solar time has been referred to the dynamical time scale derived from the
time argument of the lunar ephemeris. The duration of the day has been obtained
- from 1623
to 1860, by derivative of cubic splines fitted on individual values
of the difference between mean solar time and dynamical time (13 knots),
- from 1861 to 1955, by a 5-point quadratic convolute. More information
on the computation of the duration of the day is available in Stephenson
and Morrison (1984), with an estimation of the accuracy of these evaluations.
- From 1956
up to present, the duration of the day has been obtained from the BIH/IERS
values of UT1-TAI ; the table gives annual averages.
(Terrestrial Time) is computed by integration of D values.
the level of precision of these values of the duration of the day, the
unit of the dynamical time and the unit of TAI can be considered as having
the same duration. Thus D is expressed in present SI units. The table
gives also the values of the angular velocity of the Earth's rotation
w derived from the listed values of D.