The Moon takes about 27 days to revolve once around Earth relative to the distant stars, and about 29.5 days to go through a full cycle of phases (from full Moon to full Moon).
Two relevant “months”
- Sidereal month (true orbital period): The Moon completes one 360° orbit around Earth in about 27.3 days when measured against the fixed stars.
- Synodic month (phase cycle): Because Earth is moving around the Sun at the same time, the Moon needs extra time to line back up with the Sun–Earth line, so the phase cycle (new Moon to new Moon or full Moon to full Moon) is about 29.5 days.
