Description:
Converts HA, Dec to Parallactic Angle.
Invocation
double palPa( double ha, double dec, double phi );
Arguments
ha =
double (Given)
Hour angle in radians (Geocentric apparent)
dec = double (Given)
Declination in radians (Geocentric apparent)
phi = double (Given)
Observatory latitude in
radians (geodetic)
Returned Value
palPa = double
Parallactic angle in the range -pi to
pi.
Notes:
-
The parallactic angle at a point in the sky is the position angle of the vertical, i.e. the angle between the
direction to the pole and to the zenith. In precise applications care must be taken only to use
geocentric apparent HA,Dec and to consider separately the effects of atmospheric refraction and
telescope mount errors.
-
At the pole a zero result is returned.
Copyright © 2012 Science and Technology Facilities Council.
Copyright © 2014 Cornell University.
Copyright © 2015 Tim Jenness