heyoka.model.era#
- heyoka.model.era(time_expr: expression = heyoka.time, eop_data: eop_data = eop_data()) expression #
Earth rotation angle.
Added in version 7.3.0.
This function will return an expression representing the Earth rotation angle (ERA) as a function of the input time expression time_expr. time_expr is expected to represent the number of Julian centuries elapsed since the epoch of J2000 in the terrestrial time scale (TT). eop_data is the Earth orientation parameters dataset to be used for the computation.
The ERA is modelled as a piecewise linear function of time, where the switch points are given by the dates in eop_data. Evaluation of the ERA outside the dates range of eop_data will produce a value of
NaN
.The ERA is returned in radians, reduced to the \(\left[0, 2\pi\right]\) range.
- Parameters:
time_expr – the input time expression.
eop_data – the EOP data to be used for the computation.
- Returns:
an expression for the ERA as a function of time.