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Clarification note:
In any particular year any given star will have a maximum altitude above the horizon when it's due south, ie on the observer's meridian (northern hemisphere).
Where I've referred to summer/winter solstice and Orion/Betelgeuse it's because Orion transits the meridian around midnight at the winter solstice and midday at summer solstice in our era.
In winter I rise at sunset
In summer I rise at dawn
In autumn I rise at midnight
In spring I rise at noon
2080AD falls out when we seek the year that Betelgeuse transits the meridian at noon on summer solstice at its maximum possible altitude in this precessional cycle, because that's when Orion is 'crowned' by the Sun at the height of each of their respective powers.
If we choose a slightly different methodology, that of "in which year does Betelgeuse have a RA of 6h 0 0s" (implying it shares the same meridian as the summer solstice colure - by definition 6h), then we end up with a date of 2089AD instead.
9 years in 25920 isn't a very large error bar, and I'm working within the limitations of the software I have to hand which certainly isn't sophisticated enough to account for all the variables that govern precessional movements, so I'm comfortable with picking 2080AD as the turning point.
The cardinal points of the sky (solstices and equinoxes) are - as of Summer Solstice 2008 - now within one degree of where they will be at Orion's turning point, and every full moon from then until 2080 takes them a shade more than 4" of arc closer.
Tick, tick, tick, ~1" a week, and exactly 883 lunations to go as of 28th Jan 2009.
--
simon
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