Define full moon and new moon .
A full moon is the lunar phase. We know that the sun is very much bigger than the earth and moon or any of the planet. We see different sizes/phases of moon such as new moon or full moon because of the relative portion of the moon illuminated by sun as seen by an observer. A full moon occurs when the moon is completely illuminated as seen from the earth i.e. when the Moon is in opposition with the Sun . Similarly new moon occurs when the moon is obscured by the earth's shadow. Your friend has given wonderful illustrations above. You may refer to them.