Oddly enough, Pluto has major significance for the philosophy of Astrology. Before the seventeenth century, the basis of Astrology was clear and virtually universally agreed. A body gained Astrological significance through three qualities - firstly its visibility, (much of the language of Astrology is still based on 'seeing' or 'viewing' - such as the continued use of the term 'aspect');secondly on the extent to which it moves (planets are generally taken as more significant than 'fixed' stars - though the tradition gives much more importance to fixed stars than the modern approach) and lastly brightness or luminosity - The Sun and Moon as the brightest visible bodies are the most important, followed by Venus and Jupiter and then Mars, Saturn and Mercury. Similarly the brightest stars on or near the ecliptic are seen as more important than dim stars. This philosophy also encompassed meteors and comets, seen as highly, if only temporarily, important bodies.
Now with the development of the telescope, this philosophy came to be challenged. Galileo's discovery of the moon's of Jupiter was the first revelation that there were bodies which existed but were not visible with the naked eye - there was more to creation than what we could see unaided.
The identification of Uranus as a planet (rather than a very dim star, which had occasionally been seen even in classical times) added an eighth planet, less than 100 years later there was a ninth, in Neptune (but requiring a more powerful telescope in order to see it and never visible to the naked eye).
Now both Uranus and Neptune are gas giants, so one might begin to amend the philosophy of Astrology by allowing for an additional force - gravity - and try and blend in with Newtonian (and later Einsteinian) physics.
But Pluto is not a gas giant - it's much, much smaller even in its original grossly overestimated size it was only considered about the same size as Earth. On latest data, Pluto is just over two thirds the size of Mercury and has a minimum distance from Earth of 4.28 BILLION km, compared to Mercury's 77.3 MILLION km - so on the basis of gravitational force Pluto is insignificant compared to Mercury. BUT, as Dave has posted earlier - many Astrologers will argue that size (and presumably distance) doesn't matter. But if that is the case - what does?
The Astronomical misclassification of Pluto, delayed the recognition and understanding of our nature of the solar system by 50 years - Astronomers now recognise that Pluto was the first of a new type of body - now referred to as plutoids. Pluto has caused Astronomers to rethink their knowledge and understanding.
In the same way, I think that Astrologers need to rethink - simply asserting that Pluto is important is not enough - we need a reason why. The importance lies not just for Pluto but for a host of other bodies that are continually being identified and categorised. Why is Pluto more important than Charon or Eris or any of the other bodies out there? There may be a reason for it's importance and we really do need to look. If size and distance don't matter, then how can we say that Pluto has a major effect - the effects (if real) might be down to bodies that we as yet don't know about or indeed to specks of cosmic dust.
Is human awareness a factor? Are the intense effects of Pluto transits referred to by siren85 may be some kind of psychosomatic effect - people expect an intense transit and so they get one - but no less 'real' for them.
Is it speed - the slower the pace the greater the effect, irrespective of size and distance - in which case why are the 'fixed' stars (which actually move 1 degree per 72 years, as seen from Earth) even more powerful - especially when there are far more of them than plutoids.
Or do we simply say, we don't know but we'll take it as a fact because that's our current Astrological view. Indeed in his book on Sports Astrology the traditional Astrologer, John Frawley, actually reports a Pluto effect - he says he doesn't know why it should happen because he can't find it in other branches of Astrology but that he accepts it for practical purposes.
That might practically work but it opens the door to chaos - any and every body discovered out in the Kuyper Belt must have an equal claim to such importance and there are hundreds if not thousands of them.
So why is Pluto more important than Mercury and why is Pluto more important than Eris? - The answers to both may be in Pluto's favour but how do we proceed?
