Layman's explanation: The precession of the equinox is the age-old phenomenon whereby an observer on Earth will notice that after one year (solar, tropical, equinoctial), he will not realign with the exact same point relative to the distant stars. From two to four thousand years ago observers on Earth noticed that the sun on the vernal equinox aligned with the constellation Aries, and in the last few thousand years with Pisces. Now as many know, we are at the "dawning of the age of Aquarius", meaning the sun on the vernal equinox is close to aligning with the constellation of Aquarius. This apparent backward motion of the stars (at the time of the equinox) is the precession of the equinox – whereby the equinoctial point slowly recedes through the 12 constellations of the Zodiac at the present rate of about 1 degree per 71.6 years. If this rate were constant it would take about 25,700 to 25,800 years to complete one full precession of the equinox. However, the annual rate is now speeding up, meaning the calculated length of one full cycle is getting shorter. If the observable of precession is due to an elliptical orbit of our sun around another star, as we believe, then this explains the reason for the variable rate of precession, and also tells us the full cycle will average something different than 25,700 years. All our calculations lead us to believe the period will average about 24,000 years as will be explained in a later section of this website.
Current LuniSolar Model
The current explanation for why we see this precession of the equinox is that the tug of the Sun and the Moon acting upon the Earth’s bulge (<1% wider at equator) causes the Earth to gyrate so that the pole axis slowly traces a circle in the sky over about 24,000 to 26,000 years. This model, commonly seen in textbooks, mixes nutation with precession and obfuscates the fact that these are two separate phenomenons, one local and short in duration (nutation) and one non-local and very long in duration (precession).
The Lunisolor Precession theory was originally developed before there was any formal knowledge of binary stars or their motions, and before there was any recognition that the solar system might be moving. While this theory is a good first attempt at explaining the observed phenomenon (within a static solar system), it relies on certain untested assumptions concerning the composition and stability of the earth’s core and the moon’s solidity, and has had to be modified a number of times over the years to get the calculation to fit the ever changing observable. Most astronomers do not pay attention to precession theory and consider these changes to be minor tweaks but they are actually telltale signs of the problems with current theory.
Another problem with current theory is the moon is thought to be the principal force acting upon the oblate earth. However, the moon is slowly receding from the earth (thereby theoretically producing less torque) whereas the precession rate is slowly speeding up (an indication of a greater force at work).
Few are aware of the changing rate of precession thus little attention has been paid to the fact that the observable seems to contradict the theory concerning the forces at work. To date, this issue has not been addressed in the literature.
(Update: Since we began our work the IAU has come out with resolution P03, which notes that the current lunisolar precession theory “is not consistent with dynamical theory”. We are hopeful this will lead to an acknowledgement that the precession observable includes motion of the solar system relative to the VLBI reference points – and that this recognition will advance the eventual adoption of a precession model that accounts for more than just local dynamics).
And of course the biggest failure of the current lunisolar theory is it makes no allowance for the different reference frames (a moving solar system versus fixed stars) and therefore requires that the earth change orientation relative to all objects, near and far, at the same rate. Such is not the case.