A calendar is a system of organizing days for social, religious, commercial, or administrative purposes. The term calendar can also refer to a physical record (often a paper) of such a system. Calendars can be based on astronomical events, such as the movement of the sun or the moon, or they can be based on a combination of astronomical and social factors. The Gregorian calendar, which is the most widely used calendar in the world today, is a solar calendar that was first introduced by Pope Gregory XIII in 1582. The Gregorian calendar has 12 months, with 365 days in a common year and 366 days in a leap year. The months of the Gregorian calendar are January, February, March, April, May, June, July, August, September, October, November, and December.
The Gregorian calendar is used in most countries around the world, but there are some countries that use other calendars. For example, the Islamic calendar is a lunar calendar that is used in many Muslim countries. The Chinese calendar is a lunisolar calendar that is used in China and other East Asian countries. The Hebrew calendar is a lunisolar calendar that is used in Israel. The Ethiopian calendar is a solar calendar that is used in Ethiopia. There are also many other calendars that are used around the world.
