Sun beams, moon beams, eye beams and the theory of astrological aspects

In the 5th century BCE, the philosopher Empedocles believed that when the goddess Aphrodite fashioned the human eye from the four basic elements (earth, air, fire and water), she lit a fire in the eye which emitted eye beams that made vision possible. This fanciful quasi-religious hypothesis became known as the emission or extromission theory of vision. The idea is that, thanks to Aphrodite, the human eye emits beams from its internal fire. These beams or rays emerge from the eye and travel in straight lines until they hit an object, making visual perception possible. Somehow vision occurred because eye beams from your inner fire toughed external objects and rendered them visible.

Empedocles realized that there was a logical flaw in his argument. If vision is made possible by beams emanating from the human eye, then why do we see better during the day than at night? To solve this dilemma, Empedocles postulated that there must be some interaction between eye beams and sun beams, which made day-vision a lot better.

Around 300 BCE, the mathematician Euclid (remember high school geometry?) realized that Empedocles theory was nonsense. Euclid noted that light traveled in a straight line and he wrote an entire mathematical treatise on optics and the laws of reflection. Euclid pointed out that if you look up at in the sky at night, you can immediately see the extremely distant stars. How is this possible if the eye beams have to travel to the edge of the universe and make the stars visible to you instantaneously?

Another advance in optical theory was made by Hero of Alexandria (c. CE 10-70) during the heyday of Hellenistic astrology in the same city.  Hero noted that eye beams (visual rays) traveled at great speed from the eye to objects in the environment where they were reflected by smooth surfaces but could become trapped in the uneven roughness or porousness of unpolished surfaces.

Unfortunately, the influential 2nd-century physician Galen subscribed to the emission theory of vision, which caused future generations of doctors to accept this idea.  Hellenistic astrologers also seemed to have swallowed this theory hook, line and sinker.

In their text on traditional astrology (On the Heavenly Spheres), Avelar and Rebeiro discuss the ancient theory of optics as the basis for astrological aspects. They note (p.106) that in the case of the major aspects, “the planet radiates it light, which touches another planet, allowing them to see each other and form the aspect.”

Just as the human eye has an internal fire (thanks to Aphrodite), each planet has its own internal fire which emanates planetary beams of light. To influence one another planets must be able to “see” each other. For planet A to be able to influence planet B and vice versa, the planetary rays emitted by A must reach B, and the planetary rays from B must reach A. In some cases planet A can see planet B, but not vice versa; this has to do with the theory of orbs, which are essentially each planet’s visual field.

The human eye has a horizontal visual field of about 210 degrees. Unlike the human eye, planets have much narrower visual fields (orbs), and the value varies with each planet. For example, the giant Sun has a visual field of about 30 degrees (15 degrees either side of its direct line of vision) whereas little Mercury has a visual field of only 14 degrees (7 degrees either side of its direct line of sight). For example, if Mercury is directly looking at, say, 10 degree of Virgo, then Mercury can only see another planet that lies between 3 and 17 degrees of Virgo. Any other planet in Virgo outside that range will be invisible to Mercury and thus incapable of being influenced by Mercury.

Another weird feature of planetary vision is that planets are only able to look in certain directions. They see well when they look directly ahead (180 degree aspect) or look 60, 90 or 120 degrees (sextile, square, trine) from their direct line of vision. However, if a planet looks either 30 or 150 degrees from its direct line of vision, it is staring into a blind spot (inconjunct) and can’t see anything.

An interesting corollary of this early optical theory of astrological aspects is the Arabic notion of returning, mentioned by Sahl Ibn Bishr in his Introduction to the Science of the Judgment of the Stars.  Writing about horary astrology, Sahl (James Holden translation) states:

“The explanation of return is when a planet or the Moon is joined to another planet that is retrograde or under the Sun’s beams, and it returns to it whatever it receives from it, and it destroys the matter.”

The idea is that if planet A applies to planet B, but B is Rx or under the sunbeams, then B gives back or returns to A whatever B receives from A. Now, according to aspect theory, A can only influence B if A can see B. Should B happen to be under the sun’s beams it is invisible to A, so A can’t give anything to B because A can’t see B. In this case whatever A wants to give to B returns to A simply because it can’t be given.

The case of planet B being retrograde is not as clear. It may be that a retrograde planet is debilitated and weak and thus unable to accept what A offers, so that A’s offer returns to A. Or perhaps because B is traveling backward toward A, when A’s rays reach B they strike the reflective surface of B with such force that they are reflected back to A rather than being absorbed by B.

In any case, the nonsensical emission theory of light informs the astrological theory of aspects, regardless of how silly the original theory sounds.