Precession Correction, Part One.
For many early-studies Astrologers, Precession is a concept that is only lightly familiar to them, it being linked to “the Age of Aquarius” or some other glossed-over astrological factor that doesn’t seem to apply to them. For others, “precession” is linked in their minds to the difference between the Tropical and Sidereal Zodiacs. Both of these statements are true, if incomplete.
Most simply stated, the Earth acts muck like a huge toy Top as it circles the Sun in its annual orbit. It rotates about its axis, an axis that is tilted about 23.5 degrees from the orbital plane. This tilt can be said to remain more or less leaning in one direction relative to the stars. This most obviously has an effect on our seasons as the Earth northern and southern hemispheres are tilted more towards the Sun or away from the Sun depending upon where in the annual orbital path the Earth is located. For the northern hemisphere the Earth is tilted towards the Sun in the months preceding and following June 21st.
This tilt of the Earth is square in its direction relative to the Sun in March and September, giving each hemisphere equal-length days and nights. The exact date and time of that technically equal point/time marks the spring and fall Equinox. It from the commencement of the spring equinox that the first point of Aries is established each year for the Tropical Zodiac.
Now, we have to delve a bit deeper into the Earth axial tilt. In a very, very slow manner, this “tilt” wobbles in a circle over a 25,000 year period. This results in the Aries point slowly, almost imperceptibly, changing its position from year to year relative to the fixed stars. In the last 2,000 years, the Aries point has moved backwards relative to the constellations about 25 degrees and is now near 5 degrees of Pisces when compared to the position it had two thousand years ago. This is “precession” and it amounts to about 1 degree of movement every 71.5 years.
The Tropical Zodiac is therefore some 25 degrees different in its location relative to the Sidereal Zodiac which is anchored to the star patterns in the sky above and around us. By consensus, several “authorities” have set the Sidereal Aries point relative to one or more fixed stars. Differences in this Sidereal Aries Point are quite minor in terms of degree position and each school-of-thought defends and uses its “position”.
What difference does this make to astrologers? In terms of reading a natal chart or a secondary-progression chart, the only differences between a Sidereal or a Tropical chart would relate to the “signs” being used, and any rulership or planetary affinities ascribed to that sign. The real difference in the application of the Tropical and/or Sidereal Zodiacs relates more to the use of Solar Returns, transits, Lunar Returns, and other cyclic charts. In these cases, the differences are huge! These differences will be addressed in the next part of this essay.
Copyright, Dave Monroe, June 9, 2010.