About 27 days
Explanation
The Moon is Earth's only natural satellite. Its motion involves both revolution around the Earth and rotation on its own axis. The duration of these movements is measured in two ways: the Sidereal month and the Synodic month.
Detailed Analysis:
- Sidereal Month (Revolution Period): The time taken by the Moon to complete one full revolution around the Earth relative to fixed stars is approximately 27.3 days. This is the actual orbital period. Standard geography texts often round this figure to about 27 days.
- Synodic Month (Lunar Month): The time taken for the Moon to return to the same visual phase (e.g., from New Moon to New Moon) is approximately 29.5 days. This is longer than the revolution period because the Earth is simultaneously orbiting the Sun, requiring the Moon to travel slightly extra to realign with the Sun and Earth.
- Synchronous Rotation: The Moon takes approximately the same time (about 27 days) to complete one rotation on its axis. As a result, the same side of the Moon always faces the Earth.
Key Takeaway:
The Moon's period of revolution around the Earth is approximately 27 days (specifically 27.3 days), which is distinct from the cycle of phases (29.5 days).