I predict that most of us will survive 21 Dec 2012. On the Gregorian calendar, new style. To quote my colleague, Dr. Duncan Steel
, “Trying to design calendars for use on timescales of more than a millennium makes no sense astronomically, logically or sociologically.” There is also a concise explanation of the almost innumerable historical and current calendars in Holford-Stevens
Every enterprise must have a goal. Borrowing from Duncan, the intention of the Gregorian calendar was to keep the astronomical equinox more or less on the same date as the ecclesiastical equinox, itself a total fabrication to avoid Easter occurring during Passover. The mean year length for the Gregorian calendar was the Vernal Equinox year. Note that the year by any definition is not constant by any astronomical measure; hence a mean is adopted for as long as it lasts. Which is often not very long.
Few understand what this is all about. Fewer really need to, but everything from religious observances to flying satellites depends on someone understanding well enough. You first must learn what the Equinox is. It is the line on which the Earth’s equatorial plane and the solar systems ecliptic plane intersect. The ecliptic is the plane of the Earth’s orbit about the Sun. Theoretically, each planet pulls on the rest, and the eventual equilibrium is that the planets all lie in a plane, the stable configuration.
Gravitation from other massive bodies and other sources of perturbation make this only theoretical, but close enough. Whatever that means. The Vernal Equinox is when that line points at the historical first point of Aries, now in the constellation Pisces because of precession over more than 2,000 years since this was codified. The Sun crosses the celestial equator from South to North in the Northern Hemisphere. The Autumnal equinox is when that line points toward the first point of Libra.
These crossings are harbingers of changing seasons and the “annual” observable astronomical phenomena.
Many calendrical schemes attempt to keep the equinox more or less on the same date for as long as possible. We know that this is about four years in the Gregorian scheme, but only “about.” The discrepancy between the length of day and 24 hours measured as 86,400 seconds in some standard for a second makes this scheme insufficient in several hundred years on the UTC time scale. Our current calendar will run out or have to be reset. As will all calendars, because the Equinox precesses, moving among reference constellations within the span of recorded history.
The Mayans may have done a better job than most. They had three invariant cycles: 260 days, 13 days and 20 days (their number system was essentially vigesimal – base 20). These ran concurrently. The year number was taken according to its place in the 260-day cycle despite the fact that the solar year is about 105 days longer, or five 20 day cycles plus 5. The day number advanced by 5 each year. Thus, within the 20-day cycle, only four “year bearers” were possible. Within the 13-day cycle there were 4x13=52 possible year numbers. A new calendar round was required when this happened. The Tikal Maya recognized an 18-month cycle (360 days) as well, called a “tun.” The cycle of 20’s and 13’s applied consistently led to a calendar synchronized with equinoxes for a very long time 1,872,000 days, a Long Count. The current Long Count ends on 1 (kinchiltun) 11 (calabtun) 19 (pictun) 13 0 0 0 0 4 Ahau 3 Kankin, 21 Dec 2012 on our (arbitrary) Gregorian Calendar. A new Long Count starts the 14th baktun. The world does not necessarily end. Unless Quetzocoatl wills it. Since he was Aztec, not Mayan, we are safe. Have a safe 14th baktun.