Abstract: A disk that illustrates a polar view of the earth rotatably mounted on a flat supporting base representing a celestial plane through the earth's equator. A radial arm is provided with its proximal end pivotally mounted on the center of the earth disk and its distal end fitted with a fixed disk representing the moon, such that the moon's orbit is modeled by the arm's rotation around the earth showing the near side of the moon always facing the earth. Half of the moon disk is covered by a semicircular structure representing the zone of exposure to sunlight, which can be used to explain the gradual and continuous change of moon phase as the moon revolves around the earth. Other embodiments of the invention illustrate the seasonal change of the earth's exposure to sunlight, the moon's effect on tides, and the earth's and moon's revolutions around the sun.