The reason for the phases of the moon is something that causes a lot of confusion for children and adults. There is a common belief that they are caused by the shadow of the Earth being cast onto the moon. In fact this is caused by the relative position of the moon and the earth, our view of the half of the moon being lit by the sun changes as the moon orbits us.

The changing shapes that the Moon appears to take are called phases. As the Moon orbits the Earth, light from the Sun is reflected by the Moon’s surface Half the Moon is lit, and the other half of the moon is dark. A complete cycle of phases is known as a lunar month. The Moon takes around 29.5 days to make a complete orbit of the Earth.

When the Earth is directly between the Sun and the Moon, we see a full moon. This is because the side of the Moon reflecting sunlight is facing us.

When the Moon is further on in its orbit, and less reflected light is visible, we see a last quarter moon.  When the Moon moves between the Sun and the Earth, we see no Moon at all, as the side reflecting sunlight is facing away from the Earth. This is called a new moon.

So even though it looks like the Moon is changing shape over the course of a month, it is not. The changing phases are caused by the Moon’s orbit around Earth, which changes the Moon’s position relative to the Earth and Sun.

There are many interactive simulators available online that you can use, here are a couple to get you started:

Moon Phase Simulator – Play and Watch

Lunar Simulator – Drag the moon around the earth to see how the phases change.

And yes, if you live in the Southern Hemisphere, you will see the phases moving in the opposite direction as someone in the Northern Hemisphere because they are upside down. Seriously.

There is no “Dark Side of the Moon” where the Sun never shines. There is always a dark half and light half, but if you lived on the moon you would experience roughly 14 Earth days of light and 14 days of dark. There is, however, a Far side of the Moon which we had never seen until the advent of rockets and space probes in the 1950s when we could send a probe to the other side of the moon to take photos. As it orbits the Earth the Moon rotates – taking 29.5 days to rotate once. This means it always shows the same face to the Earth, with the other side always pointing away from us.

See also : Earth Moon and Sun Papercraft Model