The phases of the moon are caused by the changing angles at which we see the sunlit portion of the moon from Earth. Here's why:

* The Moon's Orbit: The moon orbits the Earth.

* Sunlight: The sun illuminates the moon.

* Our Perspective: As the moon orbits, the angle from which we see the sunlit portion changes, creating the different phases (new moon, waxing crescent, first quarter, waxing gibbous, full moon, waning gibbous, last quarter, waning crescent).