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Astro Precession ‘Problem’ Solved

June 16, 2015

By Ken McRitchie   

Some astronomers are very fond of arguing that the signs of the zodiac are not where they should be because of Earth’s precession. Also, there should be thirteen signs instead of twelve because the Sun passes through the constellation Ophiuchus. This is a foolish argument for the following reasons.

These astronomers are too smart not to know that their argument confuses a precise coordinate system (celestial longitude used mainly by astrologers) with an arbitrary mapping convention (constellations used mainly by astronomers). They are also smart enough to know that there are twelve signs for the same pragmatic reasons there are twelve hours on a clock instead of thirteen. The four “cardinal” points, marking quadrants, are divided by three for finer detail.

With somewhat less certainty, it can be argued that science educators are smart enough to know that there are no constellations named Scorpio or Capricorn, but they incorrectly use these names when they really mean Scorpius and Capricornus (for example, see this YouTube link for “Bill Nye on Astrology”). These seemingly deliberate mix-ups are instrumental because the foolish argument is only possible by confusing signs with constellations.

About 2200 years ago during the early development of astrology, zodiac signs (in celestial longitude) and the related constellations were roughly in the same places, but precession has made them drift out of alignment. The foolish argument ignores that precession is not a problem for astrologers because astrologers do not use constellations in practice but only the individual stars, planets, and other celestial bodies.

What really makes the foolish argument most foolish is that it relies on a type of faulty thinking known as the genetic fallacy. It attacks the origins of the zodiac and astrology rather than the substance. Why should a scientist today bother to empirically test astrological claims when assailing the ancestry is easier.  As the late Carl Sagan wisely admonished, “The issue is not what faltering and rudimentary knowledge astrology came from, but what is its present validity.” Sagan and others who are critical thinkers have not succumbed to the genetic fallacy and the foolish argument.

If there are distinctly different systems in use, then why don’t all the constellations, not just Scorpius and Capricornus, have their own distinctive names? Renaming for the sake of clarity is not an insurmountable problem because the International Astronomical Union (IAU) has special committees devoted to naming conventions.

The zodiac names used by astrology for centuries will stay the same. The following suggested constellation names, formed by using the Latin genitive case, are from a quick consensus with colleagues. We would gladly leave it to IAU to officially disambiguate the problem and end the foolishness once and for all.












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About the author

Ken McRitchie is a Canadian technical writer. He is the former editor of Above & Below: Journal of Astrological Studies and is the author of Environmental Cosmology: Principles and Theory of Natal Astrology. His website is

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