Abstract: A solar energy apparatus is provided for conditioning a building. The apparatus includes a first shield having a generalized cylindrical shape with an opening along its curved surface. The first shield rotates about the perimeter of a building at a first rotational speed. A second shield, also having a generalized cylindrical shape and with an opening along its curved surface, rotates concentrically with the first shield and at a second, greater rotational speed. The speeds of each shield are preferably constant and rotation of both shields is in the same direction. The relative rotation of the shields creates an aperture that varies in size and position throughout the day and year to appropriately regulate the amount of daylight, solar energy and insulation to which the building is subjected.