How to use the pyorbital.astronomy.sun_zenith_angle function in pyorbital

def get_angles(self, vis):
        """Get sun and satellite angles to use in crefl calculations."""
        from pyorbital.astronomy import get_alt_az, sun_zenith_angle
        from pyorbital.orbital import get_observer_look
        lons, lats = vis.attrs['area'].get_lonlats(chunks=vis.data.chunks)
        lons = da.where(lons >= 1e30, np.nan, lons)
        lats = da.where(lats >= 1e30, np.nan, lats)
        suna = get_alt_az(vis.attrs['start_time'], lons, lats)[1]
        suna = np.rad2deg(suna)
        sunz = sun_zenith_angle(vis.attrs['start_time'], lons, lats)
        sat_lon, sat_lat, sat_alt = get_satpos(vis)
        sata, satel = get_observer_look(
            sat_lon,
            sat_lat,
            sat_alt / 1000.0,  # km
            vis.attrs['start_time'],
            lons, lats, 0)
        satz = 90 - satel
        return sata, satz, suna, sunz

def get_angles(self, vis):
        """Get the sun and satellite angles from the current dataarray."""
        from pyorbital.astronomy import get_alt_az, sun_zenith_angle
        from pyorbital.orbital import get_observer_look

        lons, lats = vis.attrs['area'].get_lonlats(chunks=vis.data.chunks)
        sunalt, suna = get_alt_az(vis.attrs['start_time'], lons, lats)
        suna = np.rad2deg(suna)
        sunz = sun_zenith_angle(vis.attrs['start_time'], lons, lats)

        sat_lon, sat_lat, sat_alt = get_satpos(vis)
        sata, satel = get_observer_look(
            sat_lon,
            sat_lat,
            sat_alt / 1000.0,  # km
            vis.attrs['start_time'],
            lons, lats, 0)
        satz = 90 - satel
        return sata, satz, suna, sunz

Uses pyspectral.
        """
        from pyspectral.rayleigh import Rayleigh

        (vis, red) = projectables
        if vis.shape != red.shape:
            raise IncompatibleAreas
        try:
            (sata, satz, suna, sunz) = optional_datasets
        except ValueError:
            from pyorbital.astronomy import get_alt_az, sun_zenith_angle
            from pyorbital.orbital import get_observer_look
            lons, lats = vis.attrs['area'].get_lonlats_dask(CHUNK_SIZE)
            sunalt, suna = get_alt_az(vis.attrs['start_time'], lons, lats)
            suna = np.rad2deg(suna)
            sunz = sun_zenith_angle(vis.attrs['start_time'], lons, lats)
            sata, satel = get_observer_look(vis.attrs['satellite_longitude'],
                                            vis.attrs['satellite_latitude'],
                                            vis.attrs['satellite_altitude'],
                                            vis.attrs['start_time'],
                                            lons, lats, 0)
            satz = 90 - satel
            del satel
        LOG.info('Removing Rayleigh scattering and aerosol absorption')

        # First make sure the two azimuth angles are in the range 0-360:
        sata = sata % 360.
        suna = suna % 360.
        ssadiff = abs(suna - sata)
        ssadiff = xu.minimum(ssadiff, 360 - ssadiff)
        del sata, suna