Compute (alt, az, distance) relative to the observer's horizon

        The altitude returned is an `Angle` in degrees above the
        horizon, while the azimuth is the compass direction in degrees
        with north being 0 degrees and east being 90 degrees.

def altaz(self, temperature_C=None, pressure_mbar='standard'):
        """Compute (alt, az, distance) relative to the observer's horizon

        The altitude returned is an `Angle` in degrees above the
        horizon, while the azimuth is the compass direction in degrees
        with north being 0 degrees and east being 90 degrees.

        """
        return _to_altaz(self.position.au, self.observer_data,
                         temperature_C, pressure_mbar)