Why do we see different phases of the moon?

The Moon itself does not generate light; it is lit up by the Sun. As the Moon orbits the Earth, the portion of illuminated Moon that we see changes – giving rise to the phases of the Moon. Starting at the New Moon phase, the Moon appears to expand in illumination. Once it reaches the Full Moon phase, it then seems to decrease in illumination until we reach the New Moon again after one month. Sometimes the Earth, Moon and Sun are aligned such that the Earth is directly between the Sun and the Moon. The Earth casts a shadow onto the Moon, causing a lunar eclipse. When the Moon moves directly between the Earth and the Sun, we see a solar eclipse.