"Precession"

The Changing Cycle

Before an observer positioned on a fixed point on Earth can measure or detect the phenomenon of the “Precession of the Equinoxes” and make assumptions about the length of its cycle, the observer must first of all know the exact length of Earth’s orbital period from vernal equinox to vernal equinox (i.e. the exact duration of the tropical year).

Without knowing the exact position of the equinox, which is in reality an imaginary point projected into space, precession and its assumed cycle can not be determined. Variations in stellar declinations are caused by precession, but not vice versa. Precession CANNOT be detected or measured with respect to the position of the Sun alone.

In practice, Earth’s period of revolution around the Sun is derived from Earth’s daily rotation period as measured relative to the Sun and the fixed stars. Precession is the angular difference or rotation time difference between Earth’s 360-degree rotation on its axis (tropical day) and Earth’s complete rotation relative to the fixed stars (sidereal day).

After one complete 360° revolution of the Earth around the Sun (tropical year), this daily rotation difference accumulates to approximately 50.26” (arcseconds). It takes Earth about 3.34 time seconds, and not roughly 1223 seconds, to rotate through this angle. The 1223 seconds represent an angle of approx. 50.26” in a 360° orbit period of 31,556,925.97 seconds (tropical year).

Those who claim that the tropical year represents an orbit of less than 360° (i.e. 360° minus 50.26”) already assume the existence of a celestial phenomenon (i.e. precession and its cause), which is impossible to observe just by measuring the length of the tropical year relative to the position of the Sun.

Even Hipparchus determined the length of the tropical year (equinox) as accurately as he could before he noticed the motion of the sphere of the fixed stars relative to the orientation of Earth’s rotational axis in space. Later, Isaac Newton developed a theory to explain the cause which does not exist in practice – lunisolar forces producing a wobble of Earth's rotational axis.

All periods for the assumed precession cycle are always given in tropical years, and the numbers usually range anywhere from 25 to 26 thousand years. They are based on the assumption that the celestial pole of the Earth describes a nearly perfect 360° circle in space.

Since 360° are equal to 1,296,000 arc seconds it is easy to see how a precession cycle and the precessional rate (arcsec per tropical year) are directly related:

1296000 ÷ 50 = 25920

1296000 ÷ 50.116 =25860

1296000 ÷ 50.26 = 25786

1296000 ÷ 49.846 = 26000

1296000 ÷ 51.84 = 25000

1296000 ÷ 54 = 24000

Obviously, the number 24000 (54”/year) stands out. That’s because it is not based on a 360° circle but rather on a 360° ellipse.

The fact is, no astronomical observer has ever witnessed or lived through at least one entire precession cycle. It is true that the currently observed rate of precession is approx. 50.26”/year. This doesn’t mean that the rate was the same several thousand years ago, or that it will remain the same for the next several thousand years. Nobody knows for sure yet.

It’s like an observer who lives for only two days on Earth measuring the length of the true solar day, for instance, on June 21st and June 22nd. It would be wrong for the observer to conclude that every solar day had the same length. Earth travels at different speeds in an elliptical orbit around the Sun. Hence, the length of the true solar day varies in practice. By definition, the mathematically exact “mean solar day” is based on a 360° circle and a constant speed – it is an average figure. We know because we have observed many complete cycles (solar years).

However, the period of the presumed precession cycle is calculated based on a very limited amount of more or less accurate observational data. Since the cycle is extremely long in duration and the actual path of Earth’s celestial pole in the sky is not truly known, all attempts to assign a solid figure to such a cycle appears to rest on non-solid ground. The historical information remains vague.

Yet from a celestial mechanical point of view, it is not the number or the period of the cycle that seems relevant but rather the physical cause that explains the 360° motion of the celestial pole. There is extremely clear scientific evidence that the rotational axis of the Earth does NOT precess (wobble) relative to the Sun and other objects within the solar system as the Earth makes a complete 360° orbit around the Sun each tropical year. However, Earth's celestial pole slowly changes its orientation relative to the stars. Thus, for an observer on Earth the stars change their position in the sky (declination) by approximately 47° during half a precession cycle (i.e. from winter to summer solstice) -- but not the Sun, it repeats the same yearly path in the sky! The same applies to Sirius.

In view of these astronomical facts, it seems that the Yuga cycle theory of ancient India best explains the observed phenomenon of the "Precession of the Equinoxes". For many ancient cultures, precession represents a "cycle of ages" or a cycle of changes. Perhaps we still lack the ability to comprehend it all. We just can't remember how things were 12000 years or 13000 years ago. The uncertainty of time is time itself.

January 2005

© Sirius Research Group