Abstract: An opaque open-ended cylindrical tube, with a flange on one end, has its other end connected to a surface of a platform with the axis of the cylinder normal to the surface. When rays of the sun are substantially normal to the surface, a lens causes a concentrted illumination of a group of tracking photocells carried on the surface within the cylinder. In response to the concentrated illumination, the tracking photocells provide signals that cause the platform to rotate in a direction that maintains the surface substantially normal to the rays of the sun. Additionally, outside of the cylinder and adjacent thereto, a group of acquisition photocells are shielded by the flange from the sun when the rays thereof are substantially normal to the surface. When there is a large angle between a normal to the surface and the rays of the sun, the acquisition photocells provide signals that cause the platform to rotate in a direction that reduces the angle.