A digital solar compass has a planar image sensor (5) for capturing an image of a gnomon (1) perpendicular to the plane of the image sensor. A cover (12) protects the gnomon and image sensor. A signal processor (14) is arranged to determine the angle of a shadow cast by the sun and the gnomon from the image captured by the planar image sensor. The gnomon (1) may be mounted directly on the planar image sensor (5) or the shadow may be formed on a diffuser sheet (3) and projected onto the image sensor (5) using a lens (4).