The calendar is a visual scheme for the measurement of time. The calendar has been one of the most primitive forms for the distinction of the passage of past and future time and subsequently used for the organization of important festivities and events.
The word calendar only emerged around the year 1175 and comes from the Latin calendārium which means ‘book of accounts’ that derives from the word calend which was the day when the term for the payment of some debt expired.
The first calendars used the record of cycles in nature to orient and define times such as the course of days (day-night), the cycles of the moon (month), the seasons of the year (annual cycle), movement of the stars (astrological cycles), etc.
The calendars serve for a group of people to reach a collective consensus on the calculation of time and the setting of festivities, obligations and any event considered important in said society.
There are several types of calendars not being exclusive but complementary, that is, more than one type of calendar can be used simultaneously. The best known calendars are:
- The lunar calendar: each lunar month consists of a cycle of the moon going through the 4 phases of the moon: new moon, crescent moon, full moon and finally waning quarter moon. A year is composed of 13 months and each month is composed of 28 to 29 days. According to this calendar, for example, the Chinese calendar is governed .
- The solar calendar: it is made from the sun’s cycles, that is, according to the position of the Earth around the sun. A solar year is the complete cycle of our planet Earth around the sun that lasts 365 days. The current western calendar is the Gregorian calendar.
- The Inca calendar: each year consisted of 12 months of 30 days and was based on both lunar cycles and solar cycles. These calendars are also called mixed calendars.
Calendar is also used as a synonym for programming, chronology or list of activities of an organization, institution or event such as the school, university or academic calendar that identifies the dates of delivery times and / or academic activities in general or an ovulation calendar which schematizes the behavior of the ovule defining the fertile period of the woman.