What causes the phases of the moon starting with the New Moon?

Answer 1

The revolution of the moon around the earth causes the the phases of the moon.Phases of the moon are nothing but the changing positions of the moon in relation to the earth and the sun.On new moon days,the moon lies between the earth and the sun and therefore it seems dark from the earth.
From the new moon to the full moon period,the moon waxes and during this period, if the sun and the moon are separated by 90 degrees when viewed from the earth,the phase is called first quarter.
On full moon days,the full face of the moon,illuminated by sunlight, is visible from the earth and on this day, the earth lies between the sun and the moon.
From the full moon to the new moon period, the moon wanes and during this period,if the the sun and the moon are separated by 90 degrees (when viewed from the earth),then this phase is called last quarter.

Answer 2

The angle that we view the moon from earth and the illumination angle of the sun's light.

Answer 3

I think the sun blocks the moon when it is new.