how and why do phases of the moon appear?

Answer 1

The Moon always keeps the same face to the Sun.....
Therefore when it is between the Sun and the Earth it is a "New Moon" and "Not Visible"
When it is opposite the Earth and the Earth is positioned between the Moon and the Sun it is a "Full", ie. A round bright orb.,Moon
When it is traveling towards the Sun it is Waning and when it is between the position of a New Moon and Full Moon it is Waxing....in either position it is either a growing Crescent Moon or a declining Crescent Moon...

Answer 2

The changing positions of the moon in relation to the earth and the sun are known as different phases of the moon.
When the earth lies between the sun and the moon,full face of the moon,illuminated by sunlight, is visble from the earth and this(phase) is called full moon.
On new moon (which is another phase) 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.During this waxing period,half the moon will be seen when the moon and the sun are separated by 90 degree when viewed from the earth.This position is called first quarter.Half moon will be again seen under similar position ( 90 degree)of the sun,earth,and moon during wanning period.This position of the moon is called last quarter.

Answer 3

As the moon orbits the earth , we see only the part of the moon that is reflecting the light of the sun .
If the moon shows in line with where the sun set , we will see only a tiny sliver of it .
When we face the moon with our backs turned toward where the sun set , we will see the entire "full" moon .
When we face the moon with our shoulder aimed toward the place where the sun set , we'll see only half of the moon . The other half is in darkness .