months of the Maya Calendar. |
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So familiar has the calendar become that people tend to forget that it, too, had to be invented. Early farmers needed to know when to plow and sow ahead of rainy seasons, and to time other seasonal activities. Early priests in Babylonia, Egypt, China and other countries, even among the Maya in America, examined therefore the motions of the Sun, Moons and planets across the sky, and came up with a variety of calendars, some still in use. The DayThe basic unit is obviously the day: 24 hours, 1440 minutes, 86400 seconds, each second slightly longer than the average heartbeat. The day is defined by the motion of the Sun across the sky, and a convenient benchmark is noon, the time when the Sun is at its highest (i. e. most distant from the horizon) and is also exactly south or north of the observer. "One day" can therefore be conveniently defined as the time from one noon to the next. A sundial can track the Sun's motion across the sky by the shadow of a rod or fin ("gnomon") pointing to the celestial pole (click here for construction of a folded-paper sundial), allowing the day to be divided into hours and smaller units. Noon is the time when the shadow points exactly south (or north) and is at its shortest. What then is the period of the Earth's rotation around its axis? A day, you say? Not quite. |
In Iran, the biggest holiday is Nowruz, New Year's Day.... It always begins on the first day of spring at the exact moment of the equinox. This means that every year Nowruz begins at a different time. One year it might be March 21 at 5:32 A.M., while the next year it might occur on March 20 at 11:54 P.M. Every Iranian knows the exact moment the jubilation begins. The festivities are preceded by weeks of preparation. Everyone thoroughly cleans his house, buys or makes new clothes, and bakes traditional pastries. A ceremonial setting called a haftseen, which consists of seven symbols beginning with the sound "s," is displayed with other meaningful objects like mirror, colored eggs, and goldfish in a bowl. The objects represent health, renewal, prosperity, fertility and the usual universal hopes shared by people at any New Year's celebration.... For Nowruz, most businesses close and the streets are deserted. For twelve days after equinox, people visit relatives and friends, always starting with the eldest. Once all the elders have been visited, they in turn visit the younger members of the family. At every house, a tray of homemade sweets is offered along with wishes for the new year. Children receive money, always in the form of brand-new bills. I assume that since the wave of immigration after 1980 [the revolution in Iran] banks in America have noticed a sudden increase in demand for crisp bills in the month of March. [from "Funny in Farsi -- A Memoir of Growing Up Iranian in America" by Firoozeh Dumas, 187 pp., $21.95, Villard Books 2003. A charming, sunny book about growing up in two cultures.] |
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."
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 thatIn 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,
Exploring Further: Web site about the calendar. Another one, here.
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? *** Doomsday 2012? *** Still more about 2012! *** 2012 and a distant companion of the Sun *** Shift of Earth Axis in 2012? |
Optional: #6a The Jewish Calendar
Next Stop: #7 Precession of the Equinoxes
Timeline Glossary Back to the Master List
Author and Curator: Dr. David P. Stern
Mail to Dr.Stern: stargaze("at" symbol)phy6.org .
Last updated: 9-17-2004