The invention relates to a sunshine digital south finding instrument-starlight digital north finding instrument, which is a novel device applied to mobile carriers (various vehicles and ships) to measure the right south direction or the right north direction of the earth. The device consists of an instrument structure and an electrical control part. The direction-finding principle of the device comprises the following steps that: a sunshine receiver or a starlight receiver receives and irradiates an optical signal on an optical sensor; the optical sensor converts the optical signal into an electric signal and outputs the electric signal to a controller; and an azimuth angle is displayed at a current certain moment through preamplification, A/D conversion, data processing and calculation. If the position of the carrier changes, the controller can automatically search and track the sun or star to acquire new azimuth angle data which represents a deflection angle of the mobile carrier relative to the right south direction or the right north direction at the new position. The method has the characteristics of insusceptibility of interference of magnetic field and magnetic substances, high direction-finding accuracy, low cost and automatic operation of sailing direction.