heyoka.model.elp2000_cartesian_fk5

heyoka.model.elp2000_cartesian_fk5#

heyoka.model.elp2000_cartesian_fk5(time_expr: expression = heyoka.time, thresh: float = 1e-6) → list[expression]#

Get the ELP2000 formulae (FK5 J2000 frame).

Added in version 3.2.0.

Note

A tutorial explaining the use of this function is available.

This function will return an array of expressions representing the geocentric position of the Moon according to the ELP2000 analytical model. The position is returned in Cartesian coordinates [x, y, z] referred to the mean equator and rotational mean equinox of J2000 (i.e., in the FK5 frame of J2000). The position is returned in kilometres.

time_expr is the expression to be used as a time coordinate and it must represent the number of Julian centuries elapsed since the Julian date 2451545.0 in the TDB time scale. A Julian century consists of exactly 36525 Julian days.

thresh is the theory truncation threshold: larger values produce a shorter but less precise model. A value of zero will return the full untruncated model. thresh must be a finite, non-negative value.

Parameters:

  • time_expr – the input time expression.

  • thresh – the theory truncation threshold.

Returns:

an array of expressions representing the geocentric Cartesian position of the Moon according to the ELP2000 model.

Raises:

ValueError – in case of invalid input arguments.

Contents