The moon is the Earth’s only natural satellite. As the Earth moves round the sun, so the moon in turn revolves round the Earth. As it orbits the Earth, the moon also turns on its axis. The time taken to complete one rotation is the same as that taken for one orbit- about 29 ¼ days. So the same side of the moon always faces the Earth.
The moon has no light of its own and shines only because it reflects the sun’s light. As it turns on its axis only once in a journey round the Earth, each part of its surface has first about two weeks of darkness and then about two weeks of sunlight.
When the moon comes between the Earth and the sun it is invisible because the face turned towards the Earth is in darkness and sunlight is falling on the hidden side. This is the time of “new moon”. A few days later, a thin crescent moon is seen in the western sky, as the moon advances along its orbit and the sun begins to light up the side turned towards the Earth. The crescent grows larger, as sunlight advances across the moon’s disc. At “full moon” the whole disc can be seen after which the moon wanes, or grows smaller. The moon takes a lunar month (29 ½ of our days) to go through these phases, or changes of shape.