scopesim.utils.parallactic_angle

scopesim.utils.parallactic_angle#

scopesim.utils.parallactic_angle(ha, de, lat=-24.589167)#

Compute the parallactic angle.

Parameters:

  • ha (float) – [hours] hour angle of target point

  • de (float) – [deg] declination of target point

  • lat (float) – [deg] latitude of observatory, defaults to Armazones

Returns:

parang – The parallactic angle

Return type:

float

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 target point is east (west) of the meridian.

References

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

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