Greek: Aktinobolia / Latin: Proiectio radiorum / Arabic: Maṭraḥ al-shuʿāʿ
A planet sending its aspect ray to a degree it does not occupy. In Hellenistic sources the term names the ray cast backward, against the order of the signs, in the right-hand direction.
In traditional astrology an aspect is understood as a relationship made through a planet's rays. A planet stands at one degree of the zodiac. It sends its rays from that degree to the points at a sextile, square, trine and opposition. If another planet sits at one of those points, the two planets are in aspect. Casting rays describes how a planet acts on a degree it does not itself occupy.
Medieval Arabic sources describe each planet as sending out seven rays. Three go to the right and three to the left. The right and left rays are the sextile, the square and the trine. The seventh ray falls on the opposite point.
The Introduction to the Tetrabiblos attributed to Porphyry separates two verbs. The planet that leads in the order of the signs beholds the signs that follow it. The planet that follows casts its rays backward, to the signs that precede it. For example, a planet in Aries beholds a planet in Cancer, and the planet in Cancer casts a ray to the planet in Aries. Porphyry took part of these definitions from Antiochus, who lived before him. Antiochus gives the same direction. A star in Aries casts a ray to a star in Capricorn.
This direction, against the order of the signs, is the right-handed (dexter) direction. Beholding forward, in the order of the signs, is the left-handed (sinister) direction. The tradition counts the dexter aspect as stronger than the sinister one. This does not mean that the planet casting the ray prevails over the other. In the Hellenistic doctrine of overcoming, the dominant planet is the one that leads in the order of the signs. A planet in the tenth sign from another prevails over it. So the planet that receives the ray is often the one in the superior position.
Porphyry reports a view, which he credits to Thrasyllus, that casting a ray is a destruction. This view belongs to the length of life technique and concerns destructive (anaeretic) points in square and opposition.
In Arabic and Latin sources the projection of rays became a term for all of a planet's aspect rays. The Arabic is maṭraḥ al-shuʿāʿ and the Latin is proiectio radiorum. A lost Kitāb maṭraḥ al-shuʿāʿ (Book of the Projection of Rays) by Māshāʾallāh is known because Abū Maʿshar refers to it. In the eleventh century the Andalusian mathematician Ibn Muʿādh al-Jayyānī devoted a separate work to the subject.
In these sources the projection of rays is a problem of calculation. The astrologer computes the degree where each right and left ray of a planet falls. In the simplest method, 60, 90 and 120 degrees are subtracted from or added to the planet's longitude. The subtracted rays are the right rays and the added ones are the left rays. Authors such as Ibn Muʿādh measured these arcs on the celestial equator instead of the ecliptic. With this method the degree where a ray falls depends on the ascendant, the planet's position and the geographic latitude.
In the same tradition the projection of rays is treated together with tasyīr, that is, primary directions. A direction takes into account not only a planet's own degree but also the points where its aspect rays fall.
Being under the Sun's rays concerns a planet's closeness to the Sun. There the rays are the Sun's light, and the planet becomes invisible in it. Casting rays describes each planet's own aspect ray. The two terms share a word but they are different concepts.
Aversion (aversio) is the case where no ray arrives at all. Counting from a planet's sign, the 2nd, 6th, 8th and 12th signs receive no ray from it. The planet does not see these signs and casts no ray to them.
Let Saturn be in Capricorn and the Sun in Aries. Capricorn comes three signs before Aries in the order of the signs. The Sun casts a ray backward to Saturn in Capricorn by a dexter square. Saturn looks forward to Aries and sees the Sun by a sinister square. Since Saturn stands in the tenth sign from the Sun, in a Hellenistic reading it is also the planet that overcomes the Sun.