parallactic_angle

ska_sdp_func_python.util.coordinate_support.parallactic_angle(ha, dec, lat)

Calculate parallactic angle of source at ha, dec observed from site at latitude dec. With:

\[H = t - α sin(a) = sin(δ) sin(φ) + cos(δ) cos(φ) cos(H) sin(A) = - sin(H) cos(δ) / cos(a) cos(A) = { sin(δ) - sin(φ) sin(a) } / cos(φ) cos(a)\]

Parameters:

• ha – Hour angle (radians)

• dec – Declination (radians)

• lat – Site latitude (radians)

Returns:

Angle in radians