Here's why:

* Full Moon: A full moon occurs when the Sun, Earth, and Moon are aligned in a straight line, with the Earth in the middle.

* Earth's Shadow: The Earth casts a shadow into space, but during a full moon, the Moon is on the opposite side of the Earth from the Sun. This means the Moon is outside the Earth's shadow.

Therefore, the full moon is fully illuminated by the Sun and is visible from Earth.

Think of it this way: Imagine a light shining on a ball. The ball casts a shadow on the wall behind it. If you move the ball to the opposite side of the light source, it will no longer be in the shadow. The same principle applies to the Earth, Moon, and Sun.