A structure that contains apparent horizontal coordinates:
lat holds the refracted altitude angle,
lon holds the azimuth in degrees clockwise from north,
and dist holds the distance from the observer to the object in AU.
The date and time of the observation. This is needed because the returned vector object requires a valid time value when passed to certain other functions.
"normal": correct altitude for atmospheric refraction (recommended).
"jplhor": for JPL Horizons compatibility testing only; not recommended for normal use.
null: no atmospheric refraction correction is performed.
A vector in the horizontal system: x = north, y = west, and z = zenith (up).
Given apparent angular horizontal coordinates in
sphere, calculate horizontal vector.