Calendar Systems

A historical timeline

Organizing time: days, weeks, months

The structures that sort out the passage of time

Whether it starts on the first of January, mid-February or in other months, the year is organized into months, week and days, a system known as calendar. The method of ordering the years is also part of that system. How did it all start?

Celestial cycles inspired the creators of the first calendars. All early systems, except the ancient Egyptian one, were lunar. Ancient Egypt used a solar calendar.

The word calendar comes from Latin and the name given in ancient Rome to the first day of the month, calendae, when the appearance of the new moon was solemnly announced.

In classical antiquity, each hour was ruled by one of twelve goddesses and their tasks. Check our special timepiece for the current Hora in several cities.

From Julian to Gregorian calendar

Calendars have continually being altered and corrected and sometimes completely redefined.

The Western or Gregorian calendar was preceded by the Julian calendar, instituted by Julius Caesar 46 BC.

The Julian system was adjusted by Pope Gregory XIII in 1582, who eliminated the accumulated error caused by a faulty calculation of the length of a year. Its recurrence was avoided by restricting century leap years to those divisible by 400.

in 1752, Britain and its colonies adopted the Gregorian calendar. 3 September became 14 September and the same time the beginning of the year was put back from 25 March to 1 Jan.

Russia did not adopt it until the October Revolution of 1917, so the event (25 Oct in 1917) is currently celebrated on 7 November.

Jewish calendar

The Jewish calendar is a complex combination of lunar and solar cycles, varied by considerations of religious observance. A year may have 12 or 13 months, each of which normally alternates between 29 and 30 days. The New Year (Rosh Hashanah) falls between 5 Sept and 5 Oct.

Chinese calendar

The Chinese calendar is lunar, with a cycle of 60 years. Both the traditional one and, from 1911, the Western calendar are in use in China.

Muslim calendar

The Muslim calendar, also lunar, has 12 months of alternately 30 and 29 days, and a year of 354 days. This results in the calendar rotating around the seasons in a 30-year cycle.

Months of the year

The lunar month (period between one new moon and the next) naturally averages 29.5 days, but the Western calendar uses for convenience a calendar month with a complete number of days, 30 or 31 (February has 28). For adjustments, since there are slightly fewer than six extra hours a year left over, they are added to Feb as a 29th day every fourth year (leap year). Century years are excepted unless they are divisible by 400. For example, 1896 was a leap year. 1900 was not. 2000 was a leap year.

The month names in most European languages were probably derived as follows: January from Janus, Roman god; February from Februar, Roman festival of purification; March from Mars, Roman god; April from Latin aperire, 'to open'. May from Maia, Roman goddess; June from Juno, Roman goddess; July from Julius Caesar, Roman general; August from Augustus, Roman emperor; September, October, November, December (originally the seventh-tenth months) from the Latin words meaning seven, eight, nine and ten, respectively.

Days of the week

In English, The days of the week are: Monday named after the Moon; Tuesday from Tiu or Tyr, Anglo Saxon or Norse god; Wednesday from Woden or Odin, Norse god; Thursday from Thor, Norse god; Friday from Freya, Norse goddess; Saturday from Saturn, Roman god; and Sunday is named after the Sun.

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