What is the length of a lunar cycle?

The length of a lunar cycle, often referred to as a synodic month, is approximately 29.53 days. This measurement represents the time it takes for the Moon to return to the same phase, such as from one full moon to the next. This period is influenced by the Earth’s motion around the Sun, which causes the Moon to take a bit longer to align with the Sun and Earth again during its orbit.

Other options, while related to lunar cycles, do not accurately define the synodic month. For example, the sidereal month, which is the time it takes the Moon to complete one orbit around the Earth relative to distant stars, is about 27.32 days. This difference occurs because, during the Moon's orbit, the Earth is also moving in its orbit around the Sun. The lunar cycle as experienced in terms of phases (from new moon to new moon) accounts for this additional time. Thus, the correct answer reflects the average duration of the complete lunar cycle based on the phases observed from Earth.