to offer an explanation for the phenomenon, and merely present a description, drawing the different shapes of the moon observed in the sky over a lunar month, although their illustrations are not always consistent with what is actually seen. Figure 1 shows drawings made by students to explain the lunar phases.Different attempts to explain these difculties have suggested that they may be related to the only explanation of the phenomenon that appears in most books and audio-visual resources: That it is based on the Moon’s movement in space, facing to the Earth a different part of the half illuminated by the Sun. Understanding this explanation of the phenomenon requires visuospatial ability, previous knowledge, and the superimposition of two different points of view, one from outside the Earth, and one from the Earth’s surface: Conceptualizing what causes moon phases requires a highly complex thinking. First of all, students should know the rotating and revolving motions of the moon and the earth and their relative positions to the sun while they move. Second, they should know that the moon is lit by the sun and we can see only the illuminated portion of the moon by the sun. And that this illuminated portion differs in shape as the position of the earth and the moon system changes relative to the Sun. To make a sound understanding of the cause of lunar phases, students should synthesize all these information, and be able to construct a three dimensional image of this trio and their relative motions in their minds (Bayraktar, 2009. p. 12).Therefore, to explain the lunar phases in this way implies that “ you have to change perspective, going to outer space from a point of view on the Earth’s surface” (Subramaniam and Padalkar, 2009. p. 18). However, many pupils and teachers do not have the capacity to work from a perspective that is different from that of a terrestrial observer (Suzuki, 2003). At the same time, the construction of a mental model