The invention provides a solar tracking system for controlling the alignment of an instrument with respect to the sun, the instrument having a solar radiation receiver and a solar radiation collector for collecting solar radiation and directing the radiation towards the receiver, the system having: at least first and second detectors locatable so as to move with the receiver and receive radiation from the collector, for generating respective first and second output signals according to their respective exposure to solar radiation from the collector; a comparison means for comparing the first and second outputs and producing a comparison signal indicative thereof; and control means for controlling the alignment of the instrument according to the comparison signal.