It's a bit tricky to say exactly what percentage of the Moon is lit by the sun at any given time, because it constantly changes! Here's why:

* Lunar Phases: The Moon's phases (new moon, crescent, full moon, etc.) are caused by the changing angles of sunlight hitting the Moon's surface as it orbits the Earth.

* Changing Illumination: As the Moon orbits Earth, the portion of its surface illuminated by the sun changes, ranging from 0% (new moon) to 100% (full moon).

So, there's no single percentage! You need to know the specific lunar phase to determine the percentage of the Moon's surface illuminated by the sun.