The point in the Moon's orbit where it lies diametrically
opposite the Sun in the sky, from the perspective of an Earth-bound
observer. At this point, under normal circumstances, the Moon's face is fully illuminated with
sunlight. As at all other times, the hemisphere of the
Moon angled away from the Sun is still cast in dark shadow, but
because of the relative positions of Moon, Earth and
Sun, this shadow is hidden for a while from observers on Earth.
Because the Earth passes between the Sun and the
Moon at the time of Full Moon, it can, and often does, affect the
Moon's visibility. This occurs when the Earth actually blocks
sunlight from reaching the Moon's surface, resulting in an event
known as a Lunar Eclipse, in which the Earth's circular
shadow can be seen to move across the face of the Moon. Because of the
orbital arrangements involved, a Lunar Eclipse can only
ever occur at Full Moon.