Physics – 6.1.1 The Earth | e-Consult

The student's statement is incorrect. The Moon's phases are not caused by the Earth blocking sunlight. Instead, the phases are caused by the changing angles at which we view the sunlit portion of the Moon as it orbits the Earth.

The Moon itself does not produce its own light; it reflects sunlight. As the Moon orbits the Earth, different amounts of its sunlit surface become visible to us. The amount of the sunlit portion we see changes because the relative positions of the Earth, Moon, and Sun are constantly changing. When the Moon is between the Earth and the Sun, the sunlit side faces away from us (New Moon). As it moves in its orbit, we see more and more of the sunlit side, resulting in phases like Crescent, Quarter, Gibbous, and finally Full Moon. The phases are a result of geometry – the changing angles of illumination as viewed from Earth, not the Earth blocking sunlight.