Here they are:
Constellation  Angular Size along the Ecliptic  Duration in Years  Start Year  Shifted Start Year 
Leo  35° 30'  2556  10880 BC  10458 BC 
Cancer  20° 30'  1476  8324 BC  7902 BC 
Gemini  28°  2016  6848 BC  6426 BC 
Taurus  36° 30'  2628  4832 BC  4410 BC 
Aries  24° 45'  1782  2204 BC  1782 BC 
Pisces  37° 15'  2682  422 BC  0 
Aquarius  24° 30'  1764  2260 AD  2682 AD 
Capricornus  27° 45'  1998  4024 AD  4446 AD 
Sagittarius  33° 15'  2394  6022 AD  6444 AD 
Ophiuchus  18° 30'  1332  8416 AD  8838 AD 
Scorpius  6° 30'  468  9748 AD  10170 AD 
Libra  23° 20'  1680  10216 AD  10638 AD 
Virgo  43° 40'  3144  11896 AD  12318 AD 
Check Total  360°  25920   
I've arranged this table so that the Age of Leo appears first in the list, which corresponds to the right starting point for this Great Year (10880 BC) if we accept that the turning point of Betelgeuse in Orion marks the midpoint.
But I've also shifted forward by 422 years the start year, because my initial choice of Betelgeuse is arbitrary and there are what I feel are strong mythological clues to the Aries/Pisces boundary being tightly associated with Year 0 of the modern western calendar.
The shifting has the effect of moving the Great Year's midpoint forward 422 years as well of course, from 2080 AD to 2582 AD. That would mean the Great Year midpoint marker would not be Betelgeuse but would instead be a line almost exactly straight down the middle of Orion less than half a degree west of Mintaka  which is rather more pleasingly symmetrical.
Naturally, these precise dates are somewhat misleading  the counstellation boundaries I've used are our modern astronomical ones and I believe the ancient astronomers themselves would not have tried to impose a purely mathematical tyranny of precision on precession.
Instead I suspect they would, by watching the sky, anticipate a forthcoming change of the vernal equinox position of the Sun from one sign to the next and begin predicting and watching for exceptional astronomical events (eg sufficiently notable conjunctions) that they would use to signify the moment of change from one World Age to the next.
However flawed my approach, at least I now have a better idea of how the Great Year might have been split up into Astrological Ages based on direct observation, prediction and ritual rather than simply dividing 25920 by 12. It's interested to notice that Scorpius's angular size on the Ecliptic is tiny compared to the other signs. 13th sign Ophiuchus  often described as just encroaching into the Zodiacal band  is much more signficant and yet...
PostScript I keep coming back to the story of Moses telling the Israelites off for worshipping a golden calf (Taurus symbolism) when he's just returned from confirming that the Age of Aries (lamb symbolism) has begun. On my crude figures that should have happened in 1782 BC, putting the biblical exodus back by about 400 years from the conventional dating (though not, it seems, too far from the date of the Hyksos Kings in Egypt).

simon
