Transcript: The moon does not emit its own light. All the light we see from the moon is reflected sunlight. The phases of the moon are related entirely to the changing angle between the Sun, the Earth, and the Moon. As the Moon orbits the Earth, it moves occasionally between us and the Sun and occasionally on the opposite side of the sky. When the Moon is nearly between us and the Sun we see the new Moon because the lit face of the Moon is facing back towards the Sun. As it continues in its orbit, after about a week, we see a first-quarter Moon. The Moon is still half lit, but we only see half of the lit surface, a quarter. Another seven days and the Moon is now on the opposite side of the sky to the Sun. We see its entire half-lit surface facing back at us, the full Moon. Seven days later, a third quarter moon. Once again, the Moon is half-lit by the Sun, and we see only a half of the lit face, a quarter.