heyoka.model.delta_tdb_tt

heyoka.model.delta_tdb_tt(time_expr: expression = heyoka.time) → expression

Difference between TDB and TT.

Added in version 7.3.0.

This function will return the difference (in seconds) between barycentric dynamical time (TDB) and terrestrial time (TT) as a function of the input TDB time (expressed in seconds elapsed from the epoch of J2000).

This function is implemented following the simplified approach described in the NASA SPICE toolkit. Specifically, we assume a Keplerian orbit for the motion of the Earth, so that the TDB-TT difference is a periodic function. This approach is accurate to approximately 0.000030 seconds.

Note

Although this function nominally takes in input a TDB time, the corresponding TT time can be used in its place with no practical effects on the accuracy of the computation.

Parameters:

time_expr – the number of TDB seconds elapsed from the epoch of J2000.

Returns:

the difference (in seconds) between TDB and TT.