heyoka.model.vsop2013_cartesian_icrf

heyoka.model.vsop2013_cartesian_icrf#

heyoka.model.vsop2013_cartesian_icrf(pl_idx: int, time_expr: expression = heyoka.time, thresh: float = 1e-9) → list[expression]#

Get the VSOP2013 formulae (ICRS Cartesian state).

Added in version 0.15.0.

Note

A tutorial explaining the use of this function is available.

This function will return an array of expressions representing the Cartesian state of a planet according to the VSOP2013 analytical model. The Cartesian state consists of position and velocity concatenated in a 6-elements array [x, y, z, vx, vy, vz] referred to the ICRS. The position is expressed in AU, the velocity in AU/day.

pl_idx selects the planet and it must be one of:

  • 1: Mercury,

  • 2: Venus,

  • 3: Earth-Moon barycentre,

  • 4: Mars,

  • 5: Jupiter,

  • 6: Saturn,

  • 7: Uranus,

  • 8: Neptune,

  • 9: Pluto.

time_expr is the expression to be used as a time coordinate and it must represent the number of Julian millenia elapsed since the Julian date 2451545.0 in the TDB time scale. A Julian millenia consists of exactly 365250 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:

  • pl_idx – the input planet.

  • time_expr – the input time expression.

  • thresh – the theory truncation threshold.

Returns:

an array of expressions representing the time evolution of the Cartesian state of a planet according to the VSOP2013 model.

Raises:

ValueError – in case of invalid input arguments.

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