What is the average duration of a full moon cycle?

The average duration of a full moon cycle, known as a lunar month, is approximately 29.5 days. This measurement reflects the time it takes for the moon to complete one full orbit around the Earth and return to the same phase, which includes the time from one full moon to the next. The lunar cycle is not exactly 30 days because the moon's orbit is elliptical and is influenced by various astronomical factors.

Choosing 29.5 days acknowledges the slight variations in timing due to these factors and accounts for the synodic month, which is the time from one new moon to the next, hence affecting the full moon cycle as well. This makes it the most accurate choice compared to the other options, which do not capture the nuances of the lunar cycle duration.