Calendopaedia - Miscellaneous Calenders

The Babylonian Calendar

The Babylonian Calendar is not particularly unsusual but is included because it was thought to be the main influence on the Egyptian, Hebrew and Islamic calendars.

The calendar was luni-solar. The year consisted of 12 months which each started at sunset when the new moon was first seen. This meant that each month was either 29 or 30 days long but their length would change from one year to the next. The new year started on the first new moon after the vernal equinox. After 19 years the cycles of the moon and the sun re-align and so an intercalary month was added at that time to bring the calendar back in line with the seasons. It would still be out by one day every 342 years (18 cycles) but it is not certain whether this correction was applied.

The Bahai Calendar

The date in the Bahai Calendar is quoted with the suffix 'BE' which stands for Bahai Era. The Bahai Era started on 21 March 1844 AD by the Gregorian Calendar. This is the date on which the Bab, the Bahai prophet, started his ministry.

The Bahai year starts on 21 March and contains 365 or 366 days just as the Gregorian Calendar. Leap years are handled in just the same way. The year consists of 19 months each of 19 days. Month 18 is followed by 4 or 5 intercalendary days which are given to feasting and present giving. The first day of each month is also a feast day. Days are considered to begin at sunset on the previous day.

The names of the months are - Splendor, Glory, Beauty, Grandeur, Light, Mercy, Words, Perfection, Names, Might, Will, Knowledge, Power, Speech, Questions, Honour, Sovereignty, Dominion and Loftiness. The intercalendary days falling between Dominion and Loftiness.

The Egyptian Calendar

The Egyptians had a lunar calendar at one time but very little is known about it. They later changed to a solar calendar which had a year that was made up of twelve months of thirty days each, and five days were added at the end. Since this meant an error of about 1/4 day per year, the starting date of the year slowly drifted forward with respect to the seasons until after 1460 years it had returned to where it started. However the Egyptians realised that the rising of the Nile, the crucial event in the Egyptian agricultural cycle, was predicted by the heliacal rising of Sirius, the brightest star in the heavens. (Heliacal rising is the time when Sirius comes out of the rays of the Sun after a period of invisibilty and is first visible on the eastern horizon at sunrise.) They then synchronised their calender with that event. The priests were given responsibility for adding the extra day when it was needed.

The French Revolutionary Calendar

The French Revolutionary Calendar, also known as the French Republican Calendar was introduced on 24th November 1793 and abolished on 1 January 1806. There were twelve months of 30 days duration followed by five or six extra days. The months were called Vendemiaire, Brumaire, Frimaire, Nivose, Pluviose, Ventose, Germinal, Floreal, Prairial, Messidor, Thermidor, Fructidor. Each month contained three weeks of ten days, the last day being the day of rest. This was the main source of discontent among the people who now had to work for nine days before having a break. The names of the days were Primidi, Duodi, Tridi, Quartidi, Quintidi, Sextidi, Septtidi, Octtidi, Nontidi, Decadi.

The additional days, five or six depending on whether it was a leap year, were known as :-

The last named was the extra day for leap years.

When the calendar was planned it was decided to make the autumn equinox the first day of the year. As the calendar was introduced on 24th November 1793 it was decided that the calendar would retrospectively start on 22 September 1792. This was the equinox and the day the French Republic was founded.

Leap years were intended to be as the Gregorian calendar with the addition of Herschel's rule that years divisible by 4000 should not be leap years. Leap years actually occurred in years 3, 7 and 11. Year 15 would have been a leap year but the calendar ended in year 14.

There was also an attempt to introduce a metric day which had ten hours. Each hour had 100 minutes and each minute 100 seconds. One reason the calendar failed has been mentioned (only one day off in every ten) but the traders did not like it as it made international trading difficult.

The Greek Orthodox Calendar

When the Orthodox church in Greece finally decided to switch to the Gregorian calendar in the 1920s, they tried to improve on the Gregorian leap year rules, replacing the "divisible by 400" rule with the following:

Every year which when divided by 900 leaves a remainder of 200 or 600 is a leap year.

This makes 1900, 2100, 2200, 2300, 2500, 2600, 2700, 2800 non-leap years, whereas 2000, 2400, and 2900 are leap years. This will not create a conflict with the rest of the world until the year 2800. This rule gives 218 leap years every 900 years, which gives an average year of 365 218/900 days = 365.24222 days, which is certainly more accurate than the official Gregorian number of 365.2425 days. However, this rule is NOT official in Greece.

The Indian Calendar

The Indian Civil Calendar was defined by the Calendar Reform Committee in 1957. Up to this time there were approximately 30 different calendars in use in India. The committee also laid down the rules for governing the religious calendar, but despite this there are still several different religious calendars in use in India.

Years are counted in the Saka Era which began with the vernal equinox in 79 AD (Gregorian). There are 12 months of 30 or 31 days and 365 or 366 days in the year. Leap years are determined in the same manner as the Gregorian Calendar. The year starts on 22 March (Gregorian) each non-leap year and 21 March in leap years. The names of the months are - Caitra, Vaisakha, Jyaistha, Asadha, Sravana, Bhadra, Asvina, Kartika, Agrahayana, Pausa, Magha and Phalguna.

The Indian Religious Calendar usually has 12 months but may have 13. This is because each month starts with the new moon. Each lunar month is given the name of the solar month in which it begins. When two new moons occur in the same solar month then the two lunar months both have the same name but with adhika placed before the name of the first month. Occasionally a solar month will occur with no new moon. When this happens the name of that solar month will not be used for a lunar month. This is known as a ksaya month. Any year which contains such a month will always also contain a adika month so that the total lunar months will never fall as low as 11. Such years occur between 19 and 141 years apart.

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