Note: When considering precession it should be kept in mind that this is a direct consequence of Earth’s own orbital instabilities and has nothing to do with the position of the Sun, which remains at the centre of the solar system.
Equinox and solstices: 1 = spring equinox (days of equal length), 2 = summer solstice (longest day), 3 = autumnal equinox (days again of equal length), 4 = winter solstice (shortest day). Key: GNP/GSP = Geographic North and South Poles, ZNP/ZSP = Zodiacal North and South Poles.
Although the true mechanism behind precession is not understood (see Section 1.5) its measurement at the spring equinox allows its variable rate to be determined and averaged. Ayanāṃśa therefore is a corrective value applied to the Sun’s current position at this equinoctial juncture – effectively reasserting a point from a former epoch – previously agreed to represent 0°, that is, the initial point of the zodiac.
Of course the exact date of this reasserted point is hotly debated, but for the sake of argument we’ll assume the last time it occurred was AD 522. Taking this date as coincident, there is currently some 20°+ difference between the Sun’s current position and its former position as of 1493 years ago.
Although the Sun’s location (at the spring equinox) has some tradition of being used to identify 0°, it is not known how long observers were aware of this position’s instability, due mostly to its imperceptible crawl. In truth, remote sky-watchers were probably more akin to seeing precession in terms of solstices23 rather than equinoxes – the latter marking an highly important yearly juncture in their calendar such as the Sun’s movement from south to north, that is, marking the longest and shortest day of the year. See the equinox and solstices diagram above.
Ancient solstices (c. 1225 bc+/–) coincide with the middle of Aslesha Nakshatra (ε Hydrae) and the start of Dhanistha Nakshatra (β Delphini) as recorded in Brihat Saṃhitā by Varāhamihira. Key: SE = Spring Equinox, SS = Summer Solstice, AE = Autumnal Equinox and WS = Winter Solstice.
This sentiment is clearly echoed in the opening quote of this chapter by Varāhamihira, taken from his Brihat Saṃhitā24 in which the esteemed astrologer notes earlier classics identifying different Nakshatras occupying the solstice positions from those of his day. Although little is revealed about the source of his information, Mihira offers no explanation as to why these positions might have changed, indicating he remained unaware of precession.
1.5 MODELS OF PRECESSION
Precession of the equinoxes and the circumnavigation of Polar Stars
Nicolaus Copernicus proposed three planetary motions. First the Earth spins upon its own axis, second it completes an annual orbit about the Sun and third it inscribes a rotational axis upon the heavens at the celestial pole, completing a single revolution every 25,920 years. This third motion, now called nutation, was thus termed ‘The Great Year’ and featured heavily in the mystery schools25 of the ancient world.
The phenomenon of precession plays a pivotal role in the history of astrology and astronomy yet, to date, its explanation still remains an unsolved mystery; and while its effect might be simulated in sophisticated computer models, mechanically they remain untenable.
Although there are some interesting theories that seek to account for precession, none really seem to put the issue to bed. Arguments for and against various mechanisms are basically ‘big science’ and well beyond the scope of this work; however, presented here for readers’ interest are three interesting possibilities. Which explanation ultimately proves correct remains to be seen; but for now the jury is out.
Chandler’s wobble (polar motion)
Seth Carlo Chandler Jr (1846–1913), an amateur astronomer and businessman, first proposed his ‘wobble’ theory in 1891, having the Earth akin to a spinning top whose lessening momentum develops a slight destabilisation of spin axis. This might be likened to a child’s spinning top that develops similar properties prior to toppling or ‘when gyroscopic forces can no longer resist the hand of gravity’. He reasoned that geographically the Earth has a greater land mass north of the equator and that this subtle pear-shaped26 profile would cause its more ‘pointed’ end (or southern hemisphere) to subtly displace the Earth’s centre of gravity, producing an incremental ‘wobble’ effect.
Chandler proposed that Earth’s North Pole moved in an irregular circle of 4–16 metres in diameter over a period of about 1.2 years. This ‘eigenmode’27 was reckoned to have a six-year cycle, during which two spiralling extremes were attained – one small and one large with a 3.5-year break in between. Since its proposal, the amplitude of the effect appears to have remained inconsistent, performing a number of surprises (referred to as phase-jumps) in the last 100 years. One significant jump occurred in the 1920s followed by a similar episode in 2000.
This ‘wobble’ had been predicted to subside after a number of decades, unless some unseen force worked upon it to reinvigorate motion. This, JPL28 believed, it had uncovered in July 2000 in the form of fluctuating oceanic pressures, coupled with changes in water temperature, ocean salinity and weather patterning. The totality of these influences were proposed to contribute to at least two-thirds of the observable phenomenon.
Although this new theory looked tenable, events in November 2005 cast doubts upon this line of enquiry as further monitoring of the smaller spiralling cycles saw Earth’s spin-axis veer rather sharply at a right angle to its normal circular motion. This anomaly was completely unexpected and not predicted in any of the computer simulations.
To date, the 124-year-old free nutation model remains unexplained. The most current revision of Polar Motion was published in August 2009,29 with its investigators concluding that the historical phase-jumps were not likely to be unique and that the accrued data (so far) should be revisited and reprocessed to attain clarity in predicting future cycles.
Binary Companion Theory
A more recent, ‘extraterrestrial’, proposal by Walter Cruttenden and Vince Dayes30 draws largely upon a popular theory called luni-solar causation. This sees the Sun’s gravitational force (along with the Moon) torqueing upon Earth’s equatorial bulge, resulting in axial gyration.31 Though the original luni-solar precession model dealt largely with near and visible objects, Binary Companion Theory is an upscaled hybridisation of the effect, working in tandem with distant unseen forces. Its protagonists claim that this alternative model of the solar system (and beyond) better accommodates the observable data whilst nicely trimming away a whole swathe of previously annoying loose ends.
One troublesome factor for the luni-solar causation camp had