ALL the moon's apparent light is sunlight reflected from the moon.s surface. It follows therefore, that if the light from the sun is blocked either partially or fully by another body (in this case the Earth) that correspondingly, part, all or indeed none of the moon's surface will be illuminated according to how the Sun, Moon and Earth are aligned relative to each other. Their positions with respect to each other change during the month as the moon orbits the Earth, and thus various portions of the moon's disc are visible from night to night.