A solar calendar is a system for organizing days based on the Earth's revolutions around the Sun. It typically divides the year into months and days, aligning with the changing seasons. The most common solar calendar is the Gregorian calendar, which has 12 months and a total of 365 days, with an extra day added every four years as a leap year. This type of calendar helps people plan activities and events according to seasonal changes, such as planting and harvesting crops. By following a solar calendar, societies can better synchronize their agricultural practices and cultural celebrations with the natural rhythms of the Earth.