Why the phases of moon occurs.

Different shapes of moon that we see are the different phases of moon. The phases occurs because the sun lights up different parts of the moon as it circles around the Earth. The phases visible to us depends on the position of moon in relation to the sun and Earth.

Phases of moon are given below :

1. New moon : when the earth and the sun are on opposite sides of the moon the position of the moon which faces the earth is dark. As a result we can not see the moon. The moon in this position is called new moon. The new moon day is called amavasya. 

2. Crescent moon : when only a part of moon is illuminated by the sunlight only the part towards the earth is visible. In these positions the moon is called crescent moon.

3. Full moon : when rays from the sun fall directly on the moon it is seen as a full disc of light. This is called full moon. The full moon day is called purnima.