* The entire Moon's surface is illuminated by the Sun at some point during its orbit around Earth. The Moon doesn't have a "dark side" that never gets sunlight.
* However, we only see one side of the Moon from Earth. This is because the Moon's rotation period is the same as its orbital period around Earth. This synchronization keeps the same side of the Moon facing us.
So, here's the answer in a nutshell:
* About 50% of the Moon's surface is illuminated by the Sun at any given time. This illuminated half is what we see as the phases of the Moon.
* The other 50% of the Moon's surface is in darkness. This is the side we don't see from Earth.
Important note: There are periods when the entire illuminated half of the Moon is visible from Earth, like during a full moon. But that doesn't mean the entire Moon is lit up, just the half facing us.
