The different phases of the Moon are due to its position relative to the Earth and the Sun. As the Moon orbits the Earth, varying amounts of its illuminated half (the side facing the Sun) are visible from Earth. When the Moon is between the Earth and the Sun, we see the New Moon phase, when the entire illuminated side is away from us. As it continues to orbit, more of the illuminated half becomes visible, leading to phases such as the Waxing Crescent, First Quarter, and Waxing Gibbous, until it reaches the Full Moon, where the entire illuminated side is visible. After the Full Moon, it goes through the Waning phases, back to the New Moon. This cycle of phases takes about 29.5 days to complete.
Which of the following best describes why we see the moon at different phases?
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