A lunar calendar is a system that measures time based on the phases of the moon. Each month begins with the new moon and lasts until the next new moon, typically lasting about 29.5 days. This results in a year of approximately 354 days, which is shorter than the solar year of 365 days. Many cultures, including the Islamic and Chinese civilizations, use lunar calendars for religious and agricultural purposes. The Islamic calendar, for example, determines the dates of important events like Ramadan, while the Chinese calendar is used to celebrate festivals such as the Chinese New Year.