The moon has no light of its own and the shape it takes as it reflects sunlight varies as it orbits the earth. When the moon is in the earth's shadow it reflects no, or very little, light. This is the time of the new moon. As the moon emerges from the earth's shadow, light reflects from its righthand side and grows, first into a crescent and then a full moon. Then it wanes, with the sunlight being reflected from its left side (see Figure 9.1).
The moon spends about half its life competing with the sun for prominence in the sky (see diagram in Figure 9.2). As a rule of thumb, if the moon rises before sunset, the illuminated side will be to the west. If it rises after midnight, the illuminated side will be towards the east.
If the moon is in one of its crescent phases, then a line joining the tips of the crescent down to the horizon will point approximately southwards in the northern hemisphere and northwards in the southern hemisphere (illustrated in Figure 9.3).
The moon rises about 50 minutes later each day, and from one new moon to the next is 29.5 days (one synodical month). A new moon occurs when the sun and moon are almost opposite each other, which is why a new moon rises around sunset and sets about sunrise.
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