Calendars old and new
What is a calendar?
A calendar is a system for regulating the passing of time. Usually, a calendar determines the start and length of the year, as well as how it is divided, such as into months. The majority are based on the observation of the movement of heavenly bodies, frequently the monthly passage of the moon and the annual movement of the sun, known respectively as lunar and solar calendars. The word "calendar" itself comes from the Latin kalendae, the plural form of the word for the first day of each month in the ancient Roman calendar.
Why were calendars invented?
In the past, it was necessary to schedule economic and agrarian activities. Knowing when and where to hunt, plant and harvest was crucial - literally a matter of survival. Today calendars are largely a matter of convenience, allowing us to schedule events, keep track of anniversaries and coordinate business.
Earliest examples
Archaeological evidence in the form of rudimentary cut marks on bone, up to 30,000 years old, have been interpreted as the very earliest calendars. For more convincing examples of prehistoric calendars, we have to fast forward 25 millennia to the civilisation of Ancient Egypt.
The Egyptians used a calendar based on the rising of the star Sirius, which gave a year that was 365 days long. Ancient Mesopotamia also used a calendar of the same length. As it takes 365 days for the earth to orbit the sun, calendars of this length appear in many different cultures. Early astronomers were well aware of the correlation between terrestrial and celestial conditions, and used observation of the heavens to create a calendar which would help them predict annual cycles of weather, know the correct season to plant crops, move livestock and exploit other natural resources. Most early calendars were based on the movements of the sun or moon. The Inca and other early Andean societies based their calendars on the Mayu, a "celestial river" that we know today as the Milky Way.
In Inca society, local hereditary rulers were responsible for scheduling economic tasks and they probably developed numerous calendars appropriate to local conditions.
The Gregorian calendar
The Romans developed the Julian calendar, which was introduced in 45 BC and set the length of the year at 365 days and 6 hours. Although an improvement on existing systems, the Julian calendar was longer than the solar year. As a consequence, astronomical events like equinoxes and solstices did not occur on the same calendar date each year. In 1582, Pope Gregory XIII introduced a new system - the Gregorian calendar. A mean year in the Gregorian calendar is 365.24 days in length, and every four years an extra day is added to absorb the extra fractions. We call this a leap year. In 1752, Britain embraced the Gregorian calendar, and it remains in use in countries throughout the world, as well as being the favoured calendric tool of the international business community.
Contemporary calendars from around the world
So do all modern societies use the Gregorian calendar? No, they don't! Here are some calendars you may not be familiar with that are used by millions of people around the world:
The Islamic Calendar
- For Muslims, the calendar begins in the year of Mohammed's flight from Mecca to Mdina - the year 622 in the Gregorian calendar.
- One year consists of twelve months, of 29 or 30 days. Thus a year has 354 days, 11.25 less than a solar year.
- The Islamic New Year 1428 begins on Al Hijra, the 20 January 2007 in the Gregorian calendar.
- The ninth month is called Ramadan. During this fasting month, Muslims are called on to abstain from food, water, smoking and sex during daylight hours.
The Hebrew Calendar
- The calendar begins with creation, calculated from biblical texts as being 3760 years before the birth of Christ.
- The calendar is important for Judaism - it determines the date of Jewish holidays, the anniversary of the death of a race known as Yahrzeits, and the days on which Psalms and sections of the Torah should be read.
- The calendar year is 11 days shorter than the solar year, so an extra lunar month is added seven times in every nineteen year period.
The Ethiopian Calendar
- Known as Ge'ez in the Amharic language, the Ethiopian calendar is based on the Coptic calendar, which in turn dates back to the ancient Egyptian system.
- Each year contains twelve months, each 30 days in length, with an additional month of five or six days.
- New Year's Day is known as 1 Mäskäräm, usually falls on 11th September in the Gregorian calendar.
And the future?
Will we all use one calendar in the future? The processes of globalisation and secularisation make our calendars seem a little old fashioned. One viable alternative might be the World Calendar, a 365-day year in which each date would always fall on the same day. Developed in 1930 by Elisabeth Achelis, this is a perennial calendar consisting of 12 months of 30 or 31 days. One "intercalary day" would be added at the end of December - a world holiday. In leap years another world holiday would be added at the end of June. Dates would fall on the same day every year, and the year would consist of four equal quarters - useful for business.
But maybe calendars are an important way of keeping a link with our past. And perhaps we already have enough problems remembering birthdays and anniversaries without the confusion of a new calendar...