Expert: Steven LJ Russo - 8/1/2008

Question
I wonder if you can help me with accurate dates (eras) for the precessional
zodiac ages.

I have three computer planisphere packages that measure the 'precession of
the equinox' and each gives a slightly different value for the precessional
zodiac ages, but that is understandable.  However, I also have a very simple
plastic planisphere that charts the precession of the zodiac, and this comes
out with radically different dates to the computer software.

ie:   Constellation of Leo
Computer 10,500  to  8,000  BC
Plastic      9,000  to  6,500  BC

(More recent dates, for Pisces and Aries, are the same for both methods).

But the plastic planisphere is so simple, I cannot see where it is going wrong.  
Precession is a fairly steady and sedate affair, and the plastic planisphere
mimics these rotations rather well.

Would you have a definitive set of precessional eras for the various
constellations?

Many thanks,
Ralph Ellis

Answer
Ralph.

Sorry this took so long, but since I did not know this info off the top of my head, I took a few days to research this.

Like you, I found a small variation from computer to plastic.

In checking on my plastic version, it was in line with what you said; 9000 to 6500.

My planisphere is the "Precession of the Equinoxes" planisphere by Heifetz, Gingerich, and Mosley.

Since I know two of the three "authors", I would trust their data over any other.

But why there is a difference I do not know.

Steve