Some people claim that the Jewish custom of the Passover plate is related to the Persian haftseen. That is a ceremonial plate with seven (or six) symbolic objects, the centerpiece of the table at the Passover dinner, perhaps the most important celebration of the Jewish year, commemorating an ancient event coinciding with the spring equinox.
The Persian year itself has 12 months--the first 6 have 31 days, the next 5 have 30 days, and the last has 28 or 29, depending on whether the year is or isn't a leap year. Each month corresponds to a sign of the zodiac. The number of days in each month (if not the order of months) is therefore the same as in the Western civil calendar. The difference is in the rule for determining leap year, which is more complex. Even the original Jalali calendar was more accurate than the Gregorian one; the current version assigns 683 leap years in a cycle of 2820 years and would take two million years before it shows a one-day inaccuracy!
An interesting calendar is used by the Coptic Christian church in Ethiopia, with 12 months of 30 days each, plus a 13th short month of 5 days. A tourist brochure once lured visitors with a promise "Come to Ethiopia and enjoy 13 months of sunshine a year."
The Maya Calendar
The Maya Indians in Central America, living on the Yucatan peninsula in Mexico, Belize and Guatemala (where Maya languages are still spoken), created an extensive civilization which peaked around the years 1200-1450. They developed an early system of symbolic writing ("glyphs") and simple mathematics, using a system like ours (including the zero!) based
not on the number 10 but on 20. They did not, however, use fractions.
Their astronomy was well developed, and they noted the "zenial days" when the Sun was directly overhead ("at zenith") and a vertical stick cast no shadow. Their year had 365 days, but in the absence of leap years it slowly shifted with respect to the solstices. That year was divided into 18 named "months" of 20 days each (numbered from 0 to 19), plus the "short month" of Wayeb, whose days were considered unlucky.
Yucatan does not experience summer and winter the way middle latitudes do (e.g. Europe or most of the US), and therefore the Maya calendar was not strongly tied to the seasons the way ours is. The planet Venus received major attention, and its cycles were accurately measured by Maya astronomers. In addition the Maya also observed a "ritual year" of 260 days, consisting of 20 named "long weeks" of 13 numbered days each.
For more--much more!--see here,
here and also
here,, the last being one of a series of web pages devoted to different calendars. About the Maya and Venus, see the chapter "Bringing Culture to the Physicists", p. 313 in "Surely You're Joking, Mr. Feynman!" by Richard Feynman
The Year 2012 and all that
In the first decade of the 21st century the notion spread that some cosmic catastrophe would occur at the winter solstice (21 December) of 2012. It seems to be based on the "long count" Maya calendar, the 13th cycle of which ends that day. I have received and answered many messages on this topic, and some of that correspondence is linked below
It seems to be merely a superstition. What catastrophe, exactly? Some of my correspondents suggested the Earth may reverse rotation (contrary to laws of mechanics), may reverse magnetic polarity (as has happened in the distant geological past, though not so suddenly, and apparently with no effect on life), that an errant planet may strike ours (no evidence of it so far) or that the galaxy might produce a burst of deadly radiation as we cross its equator. A film "2012" due to be released next week is to illustrate graphically what might happen.
Not only has modern science no evidence for such calamity, but it is hard to see how the Maya could have detected the approach of any cosmic event like those mentioned (though they might have had their own superstitions!) They were a stone-age culture with no iron and therefore no idea of magnetism, no way of telling that the galaxy was a huge wheel of stars (Galileo found that with his telescope), probably no good idea that the Earth itself was a huge sphere held together by its gravity.
If you are worried, read the correspondence below, or else the article by Joel Achenbach in "The Washington Post" of 16 October 2009 posted here,
It's Not the End Of the World".
Or else, look up
Then, if you seek fantasy and entertainment, perhaps go see the film!
Web site about the calendar. Another one, here.
An inventory of calendars.
About Julius Caesar and leap days.
"Tibaldo and the Hole in the Calendar" by Abner Shimony, 165 pp, Copernicus 1998. The book tells the story of a boy in 16th-century Italy whose birthday celebration was set for one of the "lost" days, skipped over by the one-time jump in the calendar which Pope Gregory the 13th ordered. Reviewed by Stephen Battersby in Nature, p. 460, 3 April 1998, and by David Mermin in Physics Today, p. 63, June 1998.
Questions from Users:
Why does our year start on January 1?
The Stars on the Winter Solstice of 2012
More about the year 2012
*** Still more:
"Will the World end in 2012?" (a,b)
About the Maya Calendar
Global Disaster in 2012?
Still more about 2012!
2012 and a distant companion of the Sun
Shift of Earth Axis in 2012?