Calendrical systems are methods used to organize and measure time, typically based on the cycles of the Moon and Sun. Different cultures have developed their own calendars, such as the Gregorian calendar, which is widely used today, and the Lunar calendar, which is based on the phases of the Moon. These systems help people plan events, celebrate holidays, and keep track of seasons. Each calendrical system has its unique features and rules. For example, the Hebrew calendar combines lunar months with a solar year, while the Islamic calendar is purely lunar. Understanding these systems allows us to appreciate the diverse ways humans have structured time throughout history.