The Gregorian solar calendar is the calendar system most widely used today. Introduced by Pope Gregory XIII in 1582, it was designed to correct inaccuracies in the previous Julian calendar, which miscalculated the length of the solar year. The Gregorian calendar consists of 12 months, totaling 365 days in a common year and 366 days in a leap year. Each month has a fixed number of days, with February having 28 days in a common year and 29 days in a leap year. The calendar's structure helps align the calendar year with the Earth's orbit around the Sun, ensuring that seasonal events occur at the same time each year.