parallactic_angle

simcado.utils.parallactic_angle(ha, de, lat=-24.589167)[source]

Compute the parallactic angle

Parameters
hafloat

[hours] hour angle of target point

defloat

[deg] declination of target point

latfloat

[deg] latitude of observatory, defaults to Armazones

Returns
parangfloat

The parallactic angle

Notes

The parallactic angle is defined as the angle PTZ, where P is the .. math:: taneta = frac{cosphisin H}{sinphi cosdelta - cosphi sindelta cos H} It is negative (positive) if the target point is east (west) of the meridian.

References

  1. Ball: “A Treatise on Spherical Astronomy”, Cambridge 1908