That's exactly right! The phase of the moon is entirely determined by how much of its sunlit side we can see from Earth.

Here's why:

* The moon itself doesn't produce light. The light we see is sunlight reflecting off the moon's surface.

* The moon orbits the Earth. As it orbits, the angle between the sun, Earth, and moon changes. This changing angle determines how much of the sunlit side of the moon faces Earth.

* We see different phases:

* New Moon: The moon is between the sun and Earth, so we see its dark side.

* Waxing Crescent: A sliver of the moon's illuminated side becomes visible.

* First Quarter: We see half of the sunlit side, looking like a quarter of a circle.

* Waxing Gibbous: More than half the sunlit side is visible.

* Full Moon: The moon is opposite the sun, and we see its entire sunlit side.

* Waning Gibbous: The sunlit side starts to decrease.

* Last Quarter: Again, we see half the sunlit side, but the opposite side from the first quarter.

* Waning Crescent: A small sliver of the moon remains visible.

So, yes, the phase of the moon is all about the geometry of the sun, Earth, and moon, and how much of the sunlit side we can see from our perspective on Earth!