NOVELTY - The solar tracker device (10) has a mirror (16) fixedly mounted parallel to a heliostat reflecting surface (P), and an imaging device (30) having an optical axis passing through the center point of the mirror. The imaging device is connected electronically to an electronic board (20). Whenever images of the mirror center point and the target center point are not in coincidence, the electronic board is activated to rotate the heliostat reflecting surface toward an orientation for which coincidence of the images is obtained.    USE - Solar tracker device for controlling orientation of heliostat reflecting surface along two axes of rotation so as to continuously capture available sun rays to be redirected towards fixed target in order to convert solar energy into useful energy.    ADVANTAGE - Provides solar tracker whose accuracy is substantially not affected by changes in position of heliostat rotation axes. Foundation needed to fix heliostat can be simplified since stability is not an essential requirement, thus foundation costs can be substantially reduced. Solar tracker does not need tracking calibration since image of fixed target is loaded into CPU memory before installation and this image is used by pattern recognition algorithm of CPU. Heliostat motors do not need to be position-controlled, thus eliminating need for expensive motor motion controllers and electrical cables needed for power or control of heliostat. Solar tracker is not sensitive to dust, scratches and other defects on dome since image of mirror is returned by diffracting particles of dome, and dust deposited on dome would simply play same role as these diffracting particles. Solar tracker is not sensitive to accuracy of image sensing device since both images of mirror and target are formed, whenever coincidence is obtained, on same area of imaging device, so that optical distortions and/or image sensor inaccuracy do not generate offset errors.    DETAILED DESCRIPTION - A dome (24) extends between the imaging device and the mirror on one side and the sun (S) and the fixed target (12) on a second side, such that when sun rays (14) penetrate the dome, the mirror substantially reflects back these sun rays toward the dome and a portion of these sun rays are reflected back by the dome to the imaging device to form an image of the mirror whose shape defines an image of the mirror center point, and such that an image of the fixed target is formed on the imaging device through the partly transparent dome and defines an image of the target center point. INDEPENDENT CLAIMS are also included for the following:    (1) a solar tracker system for controlling the orientation of a heliostat; and    (2) a method for positioning a heliostat for tracking the sun.    DESCRIPTION OF DRAWING(S) - The drawing is a perspective view showing a solar tracker system.    Solar tracker device (10)    Fixed target (12)    Sun rays (14)    Mirror (16)    Electronic board (20)    Dome (24)    Imaging device (30)    Heliostat reflecting surface (P)    Sun (S)