type of navigational instrument that uses the position of the Sun to establish bearing. The solar compass operates somewhat like a sundial. It indicates direction by employing the angle of the shadow cast by the Sun in conjunction with a compass card, a flat disk marked with points and degrees of direction. The solar compass is useful for navigation in the high latitudes, especially near the poles, where magnetic compasses become unreliable because of unpredictable fluctuations in the horizontal component of the Earth's magnetic field. A simple form of the solar compass seems to have been devised by the Syrian Arabs of Aleppo as early as the 14th century.