why does the border between light and dark on the moon change location?

why does the border between light and dark on the moon change location?
Answer
Brief Explanations:
The Moon orbits the Earth and the Earth - Moon system orbits the Sun. As these motions occur, the angle at which sunlight hits the Moon changes. This causes the boundary between the illuminated (light) and non - illuminated (dark) parts of the Moon to shift.
Answer:
The boundary between light and dark on the Moon changes location because of the Moon's orbit around the Earth and the Earth - Moon system's orbit around the Sun, which alters the angle of sunlight hitting the Moon.