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Calendars FAQ



Frequently Asked Questions about the Christian, Hebrew, Persian, Islamic, Chinese and various historical calendars.

This FAQ about the Christian, Hebrew, Persian, Islamic, Chinese and various historical calendars was compiled and written by Claus Tondering claus@tondering.dk with numerous contributions by others.

Copyright and disclaimer
------------------------
This document is Copyright (C) 2003 by Claus Tondering.
E-mail: claus@tondering.dk.
The document may be freely distributed, provided this copyright notice is included and no money is charged for the document.

This document is provided "as is". No warranties are made as to its correctness.

-0. Introduction (Calendar FAQ)
This is the calendar FAQ. Its purpose is to give an ...
-1. What Astronomical Events Form the Basis of Calendars?
Calendars are normally based on astronomical events, and the two ...
-1.1. What are equinoxes and solstices?
Equinoxes and solstices are frequently used as anchor points ...
-2. The Christian Calendar
The Christian calendar is the term traditionally used to ...
-2.1. What is the Julian calendar?
The Julian calendar was introduced by Julius Caesar in 45 BC. It ...
-2.1.1. What years are leap years? (Julian calendar)
The Julian calendar has 1 leap year every 4 years:...
-2.1.2. What consequences did the use of the Julian calendar have?
The Julian calendar introduces an error of 1 day every 128 years. ...
-2.2. What is the Gregorian calendar?
The Gregorian calendar is the one commonly used today. It was ...
-2.2.1. What years are leap years? (Gregorian calendar)
The Gregorian calendar has 97 leap years every 400 years:...
-2.2.2. Isn't there a 4000-year rule? (Gregorian calendar)
It has been suggested (by the astronomer John Herschel (1792-1871)...
-2.2.3. Don't the Greek do it differently? (Gregorian calendar)
When the Orthodox church in Greece finally decided to switch to ...
-2.2.4. When did country X change from the Julian to the Gregorian calendar?
The papal bull of February 1582 decreed that 10 days should be ...
-2.3. What day is the leap day?
It is 24 February!...
-2.4. What is the Solar Cycle?
In the Julian calendar the relationship between the days of the ...
-2.5. What day of the week was 2 August 1953?
To calculate the day on which a particular date falls, the ...
-2.6. When can I reuse my 1992 calendar?
Let us first assume that you are only interested in which dates ...
-2.7. What is the Roman calendar?
Before Julius Caesar introduced the Julian calendar in 45 BC, ...
-2.7.1. How did the Romans number days?
The Romans didn't number the days sequentially from 1. Instead ...
-2.8. What is the proleptic calendar?
The Julian calendar was introduced in 45 BC, but when historians ...
-2.9. Has the year always started on 1 January?
For the man in the street, yes. When Julius Caesar introduced ...
-2.10. Then what about leap years?
If the year started on, for example, 1 March, two months later ...
-2.11. What is the origin of the names of the months?
A lot of languages, including English, use month names based on Latin....
-2.12. What is Easter?
In the Christian world, Easter (and the days immediately preceding it)...
-2.12.1. When is Easter? (Short answer)
Easter Sunday is the first Sunday after the first full moon ...
-2.12.2. When is Easter? (Long answer)
The calculation of Easter is complicated because it is linked to (...
-2.12.3. What is the Golden Number?
Each year is associated with a Golden Number....
-2.12.4. How does one calculate Easter then?
Under the Julian calendar the method was simple. If you know ...
-2.12.5. What is the Epact?
Each year is associated with an Epact....
-2.12.6. How does one calculate Gregorian Easter then?
Look up the Epact in this table to find the date for the Paschal ...
-2.12.7. Isn't there a simpler way to calculate Easter?
This is an attempt to boil down the information given in the ...
-2.12.8. Is there a simple relationship between two consecutive Easters?
Suppose you know the Easter date of the current year, can you ...
-2.12.9. How frequently are the dates for Easter repeated?
The sequence of Easter dates repeats itself every 532 years in ...
-2.12.10. What about Greek Orthodox Easter?
The Greek Orthodox Church does not always celebrate Easter on the ...
-2.12.11. Did the Easter dates change in 2001?
No.
-2.13. How does one count years?
In about AD 523, the papal chancellor, Bonifatius, asked a monk by ...
-2.13.1. How did Dionysius date Christ's birth?
There are quite a few theories about this. And many of the ...
-2.13.2. Was Jesus born in the year 0?
No.
-2.13.3. When did the 3rd millennium start?
The first millennium started in AD 1, so the millennia are counted ...
-2.13.4. What do AD, BC, CE, and BCE stand for?
Years before the birth of Christ are in English ...
-2.14. What is the Indiction?
The Indiction was used in the middle ages to specify the position of ...
-2.15. What is the Julian Period?
The Julian period (and the Julian day number) must not be ...
-2.15.1. Is there a formula for calculating the Julian day number?
Try this one (the divisions are integer divisions, in which ...
-2.15.2. What is the modified Julian day number?
Sometimes a modified Julian day number (MJD) is used which ...
-2.15.3. What is the Lilian day number?
The Lilian day number is similar to the Julian day number, except ...
-2.16. What is the correct way to write dates?
The answer to this question depends on what you mean by correct....
-3. The Hebrew Calendar
The current definition of the Hebrew calendar is generally said ...
-3.1. What does a Hebrew year look like?
An ordinary (non-leap) year has 353, 354, or 355 days....
-3.2. What years are leap years?
A year is a leap year if the number 'year mod 19' is one of ...
-3.3. What years are deficient, regular, and complete?
That is the wrong question to ask. The correct question to ask is: ...
-3.4. When is New Year's day?
That depends. Jews have 4 different days to choose from:...
-3.5. When does a Hebrew day begin?
A Hebrew-calendar day does not begin at midnight, but at either ...
-3.6. When does a Hebrew year begin?
The first day of the calendary year, Rosh HaShanah, on 1 Tishri ...
-3.7. When is the new moon?
A calculated new moon is used. In order to understand ...
-3.8. How does one count years?
Years are counted since the creation of the world, which is assumed ...
-4. The Islamic Calendar
The Islamic calendar (or Hijri calendar) is a purely ...
-4.1. What does an Islamic year look like?
The names of the 12 months that comprise the Islamic year are:...
-4.2. So you can't print an Islamic calendar in advance?
Not a reliable one. However, calendars are printed for ...
-4.3. How does one count years? (Islamic calendar)
Years are counted since the Hijra, that is, Mohammed's emigration ...
-4.4. When will the Islamic calendar overtake the Gregorian calendar?
As the year in the Islamic calendar is about 11 days shorter than ...
-4.5. Doesn't Saudi Arabia have special rules?
Saudi Arabia doesn't rely on a visual sighting of the crescent moon ...
-5. The Persian Calendar
The Persian calendar is a solar calendar with a starting point ...
-5.1. What does a Persian year look like?
The names and lengths of the 12 months that comprise the Persian ...
-5.2. When does the Persian year begin?
The Persian year starts at vernal equinox. If the astronomical ...
-5.3. How does one count years? (Persian Calendar)
As in the Islamic calendar (section 4.3), years are counted ...
-5.4. What years are leap years? (Persian Calendar)
Since the Persian year is defined by the astronomical vernal equinox,...
-6. The Week
The Christian, the Hebrew, the Islamic, and the Persian calendars ...
-6.1. What is the origin of the 7-day week?
Digging into the history of the 7-day week is a very ...
-6.2. What do the names of the days of the week mean?
An answer to this question is necessarily closely linked to ...
-6.3. What is the system behind the planetary day names?
As we saw in the previous section, the planets have given the ...
-6.4. Has the 7-day week cycle ever been interrupted?
There is no record of the 7-day week cycle ever having been broken....
-6.5. Which day is the day of rest?
For the Jews, the Sabbath (Saturday) is the day of rest ...
-6.6. What is the first day of the week?
The Bible clearly makes Saturday (the Sabbath) the last day of ...
-6.7. What is the week number?
International standard ISO-8601 (mentioned in section 6.6) assigns ...
-6.8. How can I calculate the week number?
If you know the date, how do you calculate the corresponding ...
-6.9. Do weeks of different lengths exist?
If you define a week as a 7-day period, obviously the answer ...
-7. The French Revolutionary Calendar
The French Revolutionary Calendar (or Republican Calendar) ...
-7.1. What does a Republican year look like?
A year consists of 365 or 366 days, divided into 12 months of 30 ...
-7.2. How does one count years? (French Revolutionary Calendar)
Years are counted since the establishment of the first French ...
-7.3. What years are leap years? (French Revolutionary Calendar)
Leap years were introduced to keep New Year's Day on ...
-7.4. How does one convert a Republican date to a Gregorian one?
The following table lists the Gregorian date on which each year of ...
-8. The Maya Calendar
(I am very grateful to Chris Carrier for providing most of ...
-8.1. What is the Long Count? (Maya Calendar)
The Long Count is really a mixed base-20/base-18 representation of ...
-8.1.1. When did the Long Count start? (Maya Calendar)
Logically, the first date in the Long Count should be 0.0.0.0.0, ...
-8.2. What is the Tzolkin? (Maya Calendar)
The Tzolkin date is a combination of two week lengths....
-8.2.1. When did the Tzolkin start? (Maya Calendar)
Long Count 13.0.0.0.0 corresponds to 4 Ahau. The authorities agree ...
-8.3. What is the Haab? (Maya Calendar)
The Haab was the civil calendar of the Mayas. It consisted of ...
-8.3.1. When did the Haab start? (Maya Calendar)
Long Count 13.0.0.0.0 corresponds to 8 Cumku. The authorities agree ...
-8.4. Did the Mayas think a year was 365 days?
Although there were only 365 days in the Haab year, the Mayas ...
-9. The Chinese Calendar
Although the People's Republic of China uses the Gregorian ...
-9.1. What does the Chinese year look like?
The Chinese calendar - like the Hebrew - is a combined solar/...
-9.2. What years are leap years? (Chinese Calendar)
Leap years have 13 months. To determine if a year is a leap year,...
-9.3. How does one count years? (Chinese Calendar)
Unlike most other calendars, the Chinese calendar does not count ...
-9.4. What is the current year in the Chinese calendar?
The current 60-year cycle started on 2 Feb 1984. That date bears the ...
-10.1. Why doesn't the FAQ describe calendar X? (Calendar FAQ)
I am frequently asked to add a chapter describing the ...
-10.2. Why doesn't the FAQ contain information X? (Calendar FAQ)
Obviously, I cannot include everything. So I have to prioritize. ...
-10.3. Why don't you reply to my e-mail? (Calendar FAQ)
I try to reply to all the e-mail I receive. But occasionally ...
-10.4. How do I know that I can trust your information? (Calendar FAQ)
I have tried to be accurate in everything I have described. If you ...
-10.5. Can you recommend any good books about calendars? (Calendar FAQ)
This is a big question because there are so many excellent books. ...
-10.6. Do you know a web site where I can find information about X? (Calendar FAQ)
Probably not....
-11. Date (Calendar FAQ)
This version 2.6 of this document was finished ...









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