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To: Lonesome in Massachussets
Don't have a really good answer but from :

Precession of the Equinoxes

I find this:

Since planetary precession due to perturbations from Jupiter and Saturn causes the perihelion of the Earth's orbit to precess, the precession of the Earth's axis relative to the Sun has a period of 21,000-22,000 y.

11,500 is aproximately half of 22,000

33 posted on 02/25/2005 12:10:14 PM PST by Ernest_at_the_Beach (This tagline no longer operative....floated away in the flood of 2005 ,)
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To: All
PRECESSION OF THE EQUINOX

The Earth's rotation axis is not fixed in space. Like a rotating toy top, the direction of the rotation axis executes a slow precession with period of 26,000 years for the entire ecliptic of our planetary bodies to travel around our sun, a trip of 360 degrees. Each one of the 12 signs of the zodiac takes about 2100 years for our solar system to pass through. Every 72 years we actually move backward 1 degree. After 2100 years we move out of one age and into another.

The precession is like a star clock that helps us date the rotations of earth in our solar system through our galaxy.

At the time of the birth of Christ we were moving out of the Age of Aries which was the Roman Empire into the Age of Pisces. That happened around 60 BC. The early Christians were aware of this and used as their symbol the 2 fishes going in opposite directions.

Since the rotation axis is precessing in space, the orientation of the Celestial Equator also precesses with the same period. This means that the position of the equinoxes is changing slowly with respect to the background stars. This precession of the equinoxes means that the right ascension and declination of objects changes very slowly over a 26,000 year period. This effect is negligibly small for casual observing, but is an important correction for precise observations.

34 posted on 02/25/2005 12:14:30 PM PST by Ernest_at_the_Beach (This tagline no longer operative....floated away in the flood of 2005 ,)
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To: Ernest_at_the_Beach
Precession of the perihelion is unrelated to precession of the equinox. I think you are saying that the phasing of the equinox and perihelion passage are important. Currently the Earth passes through the perihelion about 6 January, near the winter solstice in the Northern Hemisphere. This has the salutary effect of moderating both Summer and Winter temperature extremes in the Northern Hemisphere, where most the land mass that can accrete snow is.
47 posted on 02/25/2005 2:43:21 PM PST by Lonesome in Massachussets (Deadcheck the embeds first.)
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