full moon: The moon is orbiting the earth in one orbit. The full moon occurs when the earth rotates on the moon , just opposite to the side of the sun, so that the moon visible from the earth is fully illuminated by the sun and the moon is seen as a full circular disc . New Moon: When the moon rotates and comes between the earth and the sun, then the back of the moon which is illuminated cannot be seen and the dark side of the moon falls on our eyes , then the new moon occurs.