公历, also known as the Gregorian calendar, is the calendar system most widely used today. It was introduced by Pope Gregory XIII in 1582 to correct inaccuracies in the Julian calendar. The 公历 consists of 12 months, totaling 365 days in a common year and 366 days in a leap year, which occurs every four years. The 公历 is based on the Earth's revolutions around the Sun, with each month varying in length from 28 to 31 days. This calendar is used for civil purposes in many countries and is essential for scheduling events, holidays, and daily activities.