The Moon takes about 27.3 Earth days to complete one full rotation on its axis, which is the same amount of time it takes to orbit Earth once.
Why this number
The Moon’s rotation period is about 27.3 days when measured relative to the distant stars, a value often given as roughly 27 days in basic references. Because its rotation period matches its orbital period (a state called synchronous rotation), the same side of the Moon always faces Earth.
Rotation vs “moon day”
Sometimes a “day” on the Moon is described as about 29.5 Earth days, which refers to the time from one lunar sunrise to the next at the same place on the surface. That longer value comes from the Moon’s 27.3‑day rotation combined with Earth–Moon motion around the Sun, similar to the difference between Earth’s sidereal and solar day.
