Lithograph of an astronomical diagram showing the phases of the Moon as it orbits the Earth. The appearance of the Moon when viewed from Earth is dependent on the relative positions of the Moon, the Earth and the Sun. When the Moon is directly between the Sun and Earth, its illuminated side is invisible to us and the Moon cannot be seen from Earth. This phase is known as the New Moon. As more of the illuminated surface of the Moon becomes visible it is said to be waxing, and just under 15 days after the New Moon, it is directly opposite the Sun and is seen as the Full Moon. It then wanes, with progresively les of its surface visible until, after 29.5 days, the cycle is complete and it disappears, becoming a New Moon again.
© Science Museum / Science & Society Picture Library