Deborah Houlding cites an example and includes a diagram that indicates the moon as casting an aspect to Saturn and Mercury and which is left and right. Is the moon regarded as casting because it has the greatest velocity? Suppose Venus and Jupiter in aspect with Venus slowing, would the nature of the aspect shift from Venus casting to Jupiter one way to Jupiter casting to Venus the other during the period when Venus stations?
I see the speed of planets being mentioned in the older texts, but rarely are they clear if "faster" means "more positive" or "more different from stationary", or if they're speaking of mean motion, as indicated by Chaldean order.
Also, in that diagram, Moon square Saturn is being cast by the Moon, the dominating planet is Saturn, and it's marked as the more powerful and direct Dexter arrangement. Does that mean that aspects are by nature stronger when the slower planet also dominates? Does this mean that the effect of the aspect will express itself in saturnine ways, while the other diagram aspect, dominating moon in sinister square with Mercury, would be both less effective and more lunar than mercurial?
I have grave doubts about Deb's explanation. She bases that on the reasoning of the later medieval Astrologers, and especially Lilly. However if you look at Hellenistic and early Medieval Astrology, the situation is quite different.
A dexter aspect cast by a planet is to its right, irrespective of speed, though that will affect whether the aspect is applying or separating.
A dexter aspect is cast against the order of signs. Valens, Sahl and Masha'allah are explicitly clear on this.
A sinister aspect is cast to the left of the planet, that is in the order of signs. Consider a chart in which The Moonin Cancer is in the tenth house and Saturn in Libra is on the Ascendant. The Moon is casting a Sinister square aspect to Saturn. because Saturn lies to the left of the Moon in the chart. Saturn on the other hand is casting a dexter aspect to the Moon because the Moon lies to its right in the chart. Now rotating the chart will not alter the relative positions of Moon and Saturn. The Moon is still in Cancer and Saturn is still in Libra.
Sinister aspects are seen as stronger than dexter aspects, so the aspect cast by the Moon is stronger than the aspect cast by Saturn and the Moon overcomes Saturn. In his introduction to Astrology Sahl writes:
The square aspect is from the fourth sign and the tenth (Sahl used whole sign houses)...
and the second square aspect that is which comes from the tenth) is stronger than the first square aspect
For brevity I've missed out his references to sextiles and trines but in both cases the aspect in the direction of signs is take as the stronger one.
Now a couple of centuries afterwards Al Biruni, in
The Book of Instruction in the Elements of the Art of Astrology gives virtually the same example as Sahl but appears (because his description is not quite as explicit as Sahl's) to reverses the strength of the aspects. It seems that there was either miscopying or mistranslation between the early Medieval Astrologerrs (who seemed to know their Hellenistic Astrology) and the later ones. I know Deb denies that such a shift occurred.
I know, because I've read the thread on Skyscript, that Deb claims that the Hellenistic version isn't really what is meant by sinister and dexter and took someone who did know his Hellenistic Astrology to task fro claiming otherwise.
So you have two definitions, which are diametrically opposite of these terms. Who is right? Well it's possible to argue that the Hellenistic Astrologers who invented Astrology and Sahl and Masha'allah who used their work didn't understand their own system.
Alternatively one can try the Deb argument and claim that the two definitions are of different things. Deb bases her argument on the Solar/Lunar cycle but I think that she is really talking about another form of strength. The waxing Moon and the Waning Moon.
But consider the situation with Sun and Saturn. On Deb's argument the Sun in Cancer applying to Saturn in Libra should be overcome by Saturn and not vice versa. It seems to me that she's confusing the solar cycle of planets with the direction that aspects are cast. It's the only way to attempt yo square the versions of Lilly and Al Biruni with a rationale that yields the dexter aspect as the stronger.
Incidentally I don't expect Deb to yield on this point she follows the later Medieval approach and we either accept that the definition changed over time or we try some way of testing which is actually stronger. But there are so many variables at work that I think that would be impossible.
Incidentally my point in my original post is that Modern Astrology treats both squares (both sextiles and trines) as of equal strength and that's built into Cosmodynes but for a practitioner of Traditional Astrology the two are not equal.