Time requires a New Precession Model

As some of you might know, astronomers are currently considering a re-definition of UTC.

Given that UTC relies on astronomical observations, with the atomic second being about 3×10E-8 s shorter than the SI second, the insertion of leap seconds remains essential for the 'equation of the equinox' and for determining the position of the equinox with respect to inertial space. Therefore, UTC is based on the mean sidereal day of 86164.0905382 seconds. This primary astrodynamical constant is the absolute 360-degree rotation period of the Earth on its axis.

In an effort to justify a presumptive a priori assumption regarding the cause of the observed phenomenon of precession, astronomers claim that even in the absence of precession, Earth's rotation period with respect to the most distant quasars is about 9 milliseconds longer than the mean sidereal day. By defining such a time interval as the absolute rotation period of the Earth on its axis, one presumes a physical reality that is not proven.

On January 1, 2003 the International Astronomical Union (IAU) will implement the use of the "non-rotating origin" in the Geocentric Celestial Reference System, i.e. a point designated as the Celestial Ephemeris Origin (CEO) on the equator of the Celestial Intermediate Pole, which replaces the Celestial Ephemeris Pole. Apparently, the latter does not take account of diurnal and higher frequency variations in the Earth's orientation. Observations have shown significant variations due to nutation or oscillations of the axis of rotation. As for their cause, science has still no conclusive explanation.

It is well known that astronomers find the complexities of the civil calendar and the equinoctial cycles (tropical year & precession cycle) annoying, and hence describe the rotation of the Earth independently from its orbital motion. By replacing the geometrically defined Equinox with a cinematically defined CEO, they also want to avoid now the complexities introduced by a conventional ecliptic (the changing orientation relative to inertial space), as it supposedly plays no role in the observations of the Earth rotation. This would seem to make it a lot easier for the average amateur astronomer, who is no longer required to ponder about the cause of precession. For instance, asking disturbing questions about the length of the sidereal year for 1900.0 and why the sidereal year depends upon the adopted value of the precession, are only two such questions that need to be asked.

In a recent discussion with a well-known astrophysicist and specialist in celestial mechanics on the issue regarding the 1955 IAU action, the gentleman erroneously concluded that the sidereal year for 1900.0 is about 1224 seconds longer than the tropical year for 1900.0. He goes on to explain that,

"The sidereal year does not depend on precession. But I am one of the few astronomers still around who remembers those old IAU resolutions you quoted and why they were worded in that way, using statements that no astronomer today would agree with and few would understand. Back in 1950, quasars had not been discovered yet, and galaxies were too faint and extended to serve as anchors, so astronomers had only stars to tell what was non-rotating (i.e., to represent an inertial frame). But all visible stars participate in Galactic rotation, so they have a motion on the sky that in the 1950s was still only poorly known. As a result, back then, the tropical year was considered more observationally accurate than the sidereal year. ("Fundamental" meant the most accurately measured quantity, from which others with less precision are derived). We could observe the length of the tropical year with more accuracy than we could observe the length of the sidereal year in the 1950s and earlier. With the discover of quasars and the advent of radio telescopes to observe then relative to other sky features, we finally had a dependable non-rotating system measurable with precision perhaps three orders of magnitude more accurate than optical observations. That began to happen in the early 1960s. By the end of that decade, the situation had reversed, and has remained reversed ever since. We can now measure the sidereal year (fixed quasar to fixed quasar) with far more precision than we can measure the tropical year. The old IAU ideas you quote have been replaced, amended, and updated several times since then to take new, high-precision observation types into account. No astronomer today except a historian would look at IAU resolutions that old, and most would not even understand what they meant. When the tropical year was "fundamental" in the 1950s, the sidereal was derived from it by adding precession. Now, with the sidereal year fundamental, the tropical year is derived from it by subtracting precession. So the sidereal year no longer depends on precession, but the tropical year does."

His explanation makes one wonder why some 50 years ago astronomers even bothered to observe the stars and accurately measure their transit periods in order to determine the sidereal year for 1900.0. It seems all they had to do was to take the time interval of the tropical year that was already observed with great precision by the ancient Mayan priests.

On a different occasion, the same expert declares to a good friend of mine that direct observations reflect reality and that astronomers describe the actual, physical motions of Earth's surface and Earth's orbit relative to the Sun and relative to the stars without any assumptions about cause. However, he admits that astronomers use different definitions as well as models that include both 360° and/or 359°59'10" revolution periods:

"... when astronomers choose to use a sidereal frame as reference, then the angle for a complete revolution with respect to the fixed stars is exactly 360°, and a revolution with respect to the equinox (which moves during the year) is only 359° 59' 10". At the same time, when astronomers choose to use a tropical frame of reference, then the angle for a complete revolution with respect to the fixed stars is 360° 00' 50", and a revolution with respect to the moving equinox is exactly 360°. [...] Different frames are used for different purposes at the same time for the same problem."

He seems to imply that astronomers choose for convenience a 360 degree tropical year when plotting eclipses and the like but revert to a less than 360 degree tropical year when trying to determine star positions!

But, is it mathematically and physically possible that two different 360° circles occupy one and the same circle at the same time for the same problem? Perhaps that kind of a science can only be discussed with someone carrying around his wristwatch all day, while measuring the seconds of the day (360° motion of the hands of the clock) with respect to a salient point on the horizon instead of the number "12" on his watch.

Without accepting physical reality, astronomers continue to deceive themselves by measuring Time with two different "yardsticks".

While direct observations and the raw data on the mean transit time of Sirius reflect the reality of physical motions of celestial bodies, they may not require us to make assumptions about the cause. However, they do seriously question the validity of the various amended and updated IAU Precession-Nutation Models.

Addendum:

It is recognized that nutation, as well as minor short and long term oscillations of the Earth's axis cause measurable variations in Earth's period of rotation. Apparently, the same physical fact and principle does not apply to a precession (wobble) of the axis. Undoubtedly, not all physicists would agree with such an assumption.