2147 is the age period resulting from the current arc second speed of precession, at least according to the wikipedia article http://en.wikipedia.org/wiki/Precession_%28astronomy%29 which gives a great year of 25765 years. But the same article at http://en.wikipedia.org/wiki/Precess...nomy%29#Values gives the great year as 25772 years. It seems the equinox is now moving at a rate which would take it all the way around the zodiac in 25764-72 years. However, the rate of precession has changed over time. The wiki comments the rate of this change is now speeding up, but the exact rate and period of precession may not be computed, even for a single whole precession period, and it appears 'quasiperiodic' around 25,700 year average. The age could be a couple of years longer than 2147 years (ie up to 2150). My use of the constant is something I would like to check. If there is an alignment with the barycentre then it would be interesting to find out how this cycle has changed over the millennia. The 25920 figure is Newton's traditional approximation, based on the movement of one degree per 72 years as a round number. Graham Hancock claims that a rate of one degree per 71.7 years is imbedded in the architecture of Angkor in Cambodia.