The Moon goes round the Earth once
every 28 days. It also takes 28 days to spin once on its axis and so we always see the same
side of the Moon from the Earth. However the Moon rocks a little on its axis and so the
amount of it that is lit up by the Sun changes from night to night.
In the diagram the
inside circle shows that only one half of the Moon is lit up by the Sun. The outer one shows
how the Moon would appear in those places when viewed from Earth. The diagram is not to
scale.
You should see from the diagram that a full Moon is always seen in the
opposite part of the sky from the Sun. In other words if a full Moon and the Sun are visible at
the same time one will be rising in the east and the other about to set in the west.
