The "long count" of the Mayan Calendar repeats every 394.3 years, so you could say that it has ended many times since it was devised.
Because of the extra weekday each year, and because of leap years, identical non-leap year calendars repeat on a cycle of 6 or 11 years. Leap years repeat every 28 years. (There are only 14 different possible calendars.) The years that were the same calendar as 2012 were 1984, 1956, and 1928.
The length of most 12-year periods is 626 weeks and one day. It's that one day that puts a certain date on the subsequent weekday after twelve years, just as a certain date is on the subsequent weekday after one regular year, the length of which is 52 weeks and one day. (If there's a leap year day during the intervening year, the date will fall a weekday later.) 12-year periods that include the year 2100 will be exactly 626 weeks long, since 2100 is not a leap year, so the weekday will be the same after a twelve-year period that includes 2100. (2100 will be only the fourth year that is different from the Julian calendar since the world started switching to the Gregorian calendar in 1582; the other years that were different were 1700, 1800 and 1900.)
Only until February 28. The next day on the 2008 calendar is February 29, but the next day on the 2013 calendar is March 1. The most recent year that matches 2013 is 2002. Coincidentally, Easter falls on the same date in 2002 and 2013 as well.
There was once an ancient civilization called the Mayan civilization unlike our own. Their calendar went on for years and years, until the day the calendar ended. On December 21st, 2012, the world is supposedly going to end because the Mayan calendar ends on that day.
One way that I determine the weekday of a particular date is to enter the date into a cell in a Microsoft Excel spreadsheet and to format the cell to show the weekday. For dates before 1 January 1900 I add a multiple of 400 to the year to make the year greater than 1899 (the Gregorian calendar completely repeats itself every 400 years).The other way is to look at the year in the perpetual calendar I created for myself.
The Mayans used their Calendar to predict astronomical phenomena such as the phases and eclipses of the moon and the orbit of Venus. They also predicted the seasons. They had worked out the mathematics for the calendar about 700 years into the future until December 21, 2012, when their culture was overthrown in a war. When their mathematicians were killed, work on the calendar ended.
Each of the six regular years advanced the date by one weekday, and each of the two leap years advanced the date by two weekdays. 6 x 1 + 2 x 2 = 10. Ten days after Sunday is Wednesday.
262 in leap years that begin on Monday, Tuesday, Wednesday or Thursday 261 in leap years that begin on Sunday or Friday and regular years that begin on any weekday 260 in any year that begins on a Saturday and regular years that begin on Sunday
Every twenty-year period that begins after the 28th of February 1900 and before the 29th of February 2080 includes five leap year days. Each calendar date advances one weekday for every year plus an additional weekday for every leap year day, because every regular year consists of 52 weeks plus one day, and every leap year consists of 52 weeks plus two days. So for every date during the period specified in the first sentence, the weekday twenty years later will be the 25th weekday after the original date (20 for the number of years plus 5 for the number of leap year days equals 25).For every Saturday after the 29th of February 2080 and before the 1st of March 2100, the weekday twenty years later is Tuesday, because every twenty-year period that begins between those dates includes four leap year days (2100 is not a leap year).
almost everything... The major difference between the two calendars is the Julian calendar has 100 leap years in every 400 years, and the Gregorian calendar has 97 leap years in every 400 years. That makes the average length of a Julian calendar year 365.25 days and the average length of a Gregorian calendar year 365.2425 days. As a result, it takes only about 128 years for the Julian calendar to accumulate a full day of error, but for the Gregorian calendar to accumulate a full day of error takes about 3200 years.
The Julian calendar looses a day every 128 years. The Gregorian calendar looses a day every 3200 years.