Okay! Y'all voted, I listened, and now, I present to you the thread on aspects (what we call "aspect doctrine") that y'all asked for. Buckle in because this one's going to be a ride! #astrology #aspects
But in order to give aspects their due, we have to take a detour into classical optical theory, because the word "aspect" literally means "look at" (Latin ad, "at, to" + spectō, "I look").
So we start off with the idea that, in the astrological ball of wax, planets interact with each other by casting glances at one another. These glances in the ancient world were conceived of as an exchange of energy, and, to summarize succinctly, it was imagined...
that the human eye was emitting some kind of ethereal light, which was referred to as "lumen," which was invisible but illuminated anything it fell on. The things illuminated then returned visible light, called "lux," to the beholder, and that was how eyesight and...
optics worked in general. Galen discusses this briefly in "On the Doctrines of Hippocrates and Plato," 7.5. If we are engaged in the vision process, what we are doing is bearing "witness" to that which we are observing, and many of the ways aspects are defined in...
the traditional corpora speak of planets "witnessing" each other. @chrisbrennan7 discusses this at length in _Hellenistic Astrology_, pp. 292ff., so please refer to that text for further information on the ancient optical theory underpinning aspects.
In modern astrology, the connection to ancient optical theory is attenuated somewhat; it's as though the planets "resonate" with each other at certain angles, but remember that the ancients conceived of the planets as active agents, not as passive...
points on some kind of cosmic timepiece. The main thing to remember is that aspect configurations are directly related to the concept of vision, and it was understood that vision worked by eyes emitting lumen and receiving back lux.
We see this reflected in literature of the day, including the New Testament (Matthew 6.22-23, NRSV):
“The eye is the lamp of the body. So, if your eye is healthy, your whole body will be full of light; but if your eye is unhealthy, your whole body will be full of darkness. If then the light in you is darkness, how great is the darkness!"
Lux. Lumen. They make aspects work. Got it? But, I want to come back to the idea of resonance. To wit, there are five aspects described by Ptolemy and agreed upon in general by the astrologers of the ancient world up through the renaissance and early modern era.
These five aspects are as follows: the conjunction (0º), the opposition (180º), the trine (120º), the square (90º), and the sextile (60º). Ptolemy explains that these ratios (as they are divisions of a circle) are important precisely because they represent...
the primary divisions of the octave in music (cf. Tetrabiblos I.13). Those correlate to the unison (conjunction), the octave (opposition), the fifth (trine), and the major third (sextile).
You'll notice that I skipped over the square. If you play the note exactly halfway between the top and bottom notes of an octave, the interval that results is actually the most dissonant interval in music, the tritone (also known as a diminished fifth or...
...augmented fourth). This musical interval corresponds to the astrological square. This is whence the language of "harmonious trine" and "tense square" emerges historically, but I don't think this is commonly known (although I can't imagine Rudhyar or...
Ficino would have overlooked this, but I haven't read enough of them to have the sources on hand). For those keeping score at home, the modern equally tempered octave has twelve notes in it—but, the zodiac preceded the chromatic scale. Greek music used tetrachords: 4-note scales!
So! We've got five aspects. But theoretically, each planet emits *seven* rays of lumen, though, that can illuminate any sign where they fall and activate things within the range of their orbs. #astrology #aspects
Each planet emits one opposition, a trine to the left and to the right, a square to the left and to the right, and a sextile to the left and right. If a planet conjoins something, it's there in body, not in aspect in the strict sense, so keep that in mind.
So, suppose you're out at night looking at Mars, which is bright in the night sky right now. If we were to draw this up on a chart, we would get something like this (the chart is set to 0º Aries rising, we're ignoring houses for now). 
So Mars is going to emit seven rays that we call "partile rays," which are exact to the degree. If you're looking at Mars, the rays he emits to YOUR right are called "dexter," to YOUR left are called "sinister." So that looks like this (wheel style change for science!)
(Y'all are here for astrology, not for my graphic design skills.) So Mars is hitting a certain collection of signs with his rays, and so we say he can behold those signs. From Aquarius, Mars can behold Aries, Taurus, Gemini, Leo, Libra, Scorpio, and Sagittarius.
Mars *cannot* behold anything in Pisces, Cancer, Virgo, or Capricorn from where he sits in Aquarius. So we say those signs are "averse." Modern astrology will say that planets can behold things in averse signs through things like semisextiles and quincunxes and so on. YMMV.
William Lilly briefly mentioned the newfangled aspects in Christian Astrology but paid them very little attention in practice. Note that my insistence on the Ptolemaic is not an argument from an antiquity, but an argument from evidence and practical data.
Not just my practical data, but thousands of years' worth of astrologers' practical data.
NOW. Say that a planet is in any of the signs that Mars can behold from where he sits in Aquarius, so, let's say Jupiter. That means Mars and Jupiter are in aspect _by sign_. So, right now, Mars and Jupiter can see each other because they are in signs that can behold one another.
We call this a "sign based aspect." Planets know what each other are doing but aren't really involved in each other's affairs until they come to a degree based aspect within a sign. That would mean Mars advances to a later degree of Aquarius, to meet the square that Jupiter
is casting there. This is the exact thing that will happen not too long from now, [checks ephemeris] late in the evening of Tuesday, November 20th in Eastern time. At that moment, both Jupiter and Mars will have switched signs into Sag and Pisces, respectively, and Mars will
catch up with the place where Jupiter's sinister square falls (the one Jupiter sends to YOUR left).
Another way to think about chirality (whether an aspect is to the left or to the right) is to consider zodiacal order: sinister aspects advance in zodiacal order (meaning Jupiter casts his square forward to Pisces), dexters go backwards (Jupiter casts his other square to Virgo).
That's only in this example, of course. The problem is: all of the planets are moving! So how can we tell when a given aspect will come into effect? How long does it take them to start? To finish? The answer, my dears, is in what we call "application, perfection, and separation."
But I will have to pick up that thread tomorrow, because I'm beat from this full moon conjunct Uranus! I'm looking forward to getting into the particulars of motion, though, because motion is what makes aspects even richer. Until then! #astrology #aspects
(And yes, I'll explain that oppositions and squares are overt and tense, trines and sextiles are harmonious and flowing—and I'll explain _why_, though I already touched on it above with the reference to Ptolemy's discussion of tonal harmony.)
