I have been researching the 2012 craze. While I know it is largely a scam, I want solid data behind what I say when the subject comes up. At the 2012Science Blog I found the statement that we, as the Maya did, use multiple calendars. I hadn't thought such a thing before, so I contacted the blogger. Our discussion led me to some interesting insights. Firstly, While we do have different calendars in use by different cultures ("Civil" in the West, which is a Catholic calendar; then Chinese, Jewish and Islamic calendars used ceremonially by their various diasporas), just within the Western Civil calendar we have several ways of counting calendar time:
- Day names in a 7-day, or weekly, cycle (Sunday, Monday, etc. in English).
- Day numbers from 1-7 in the weekly cycle, but seldom used.
- Day numbers from 1-365 (or 366) in a yearly cycle. This "day count" is mainly used by merchants to calculate "shopping days until Christmas".
- Day numbers from 1-31 (or 30, 29, 28) used within a month; an irregular cycle.
- Week numbers from 1-52 in a yearly cycle, also rarely used but found in calendar/mail programs such as Lotus Notes.
- Month names in a 12-month, yearly cycle.
- Month numbers from 1-12 in a yearly cycle, mainly used for writing dates compactly.
- Season names in the yearly cycle. These are interesting, because we have at least three ways to determine a season boundary: Astronomical, Signs, and Business. Astronomically, Spring starts with the Vernal Equinox on March 21 or 22. The signs of Spring could be sighting the first robin or daffodil, or ice break-up on a river. Spring season for business purposes starts whenever garment salespeople decide to put winter coats on sale and begin filling the racks with lighter wares and seasonal items such as umbrellas.
- Business quarters, which are usually 91 or 92 days in length; Q1 begins when a business (or civil entity) begins its Fiscal Year; a cycle of four per year.
- Year numbers in a linear sequence. We have agreed-upon meanings for year numbers covering all of history since the Big Bang more than 13,000,000,000 years ago, but usually confine the writing of dates to periods beginning about 400BC with the Golden Age of Greece. Note that there is no "year zero" when using BC and AD (or BCE and CE), so 400BC equals year -399 in an undesignated count.
- Century numbers in a linear sequence. This is the twenty-first century.
- Millennium numbers in a linear sequence. This is the third millennium since 1AD began the first millennium. This convention is seldom used.
We do have a "long count" of sorts to care for. The Gregorian calendar uses a 400-year cycle to determine which leap years to skip to keep the vernal equinox in the right place. The Gregorian Year is 365.2425 days in length. However, there is still a small fraction of a day left out. There are two definitions of an Astronomical Year, the Mean Tropical Year of 365.24219 days and the Equinoctial Year of 365.24237 days. If we want to keep our calendar lined up with the former year, we'll have to make a correction by about 4810AD; for correcting to the latter year, we can wait until about 9300AD, depending on how much the day and year length have changed by then.
So sometime before 4800AD we have to decide which astronomical year to adhere to. Ultimately, we keep our calendar in sync with the sky, so that the precessing equinoxes happen on the same day (within a day or two) year after year. And the Mayan long count? It has similar significance to December 31, 1999 (or 12/31/2000 for those of us who start counting with "one"!): the last day of a significant era, but with no prophetic meaning.