Tertiary Progressions have nothing to do with Solar Arcs in terms of calculation or theory, but they are part of the family of symbolic measurement of time. Where Primary Directions were based upon the movement of one degree at the Midheaven, i.e., four minutes of time after birth, as an equation for one year of life, and where Secondary Progressions and Solar Arcs equate one day after birth with one year of life, Tertiary Progressions equate every day in the ephemeris after birth (one year of life) to one Lunar Month. The Moon becomes all-important; it is the base for this technique of time symbolism because of its high speed, about 12.5 degrees per day on average.

Tertiary Progressions can be used to “average”, to collect, to bring to a day-focus several measurements within a particular period of time. Say you have a major arc coming to partile in June, and three major “trigger” transits occurring in April and May. Then perhaps the Secondary Progressed Moon is getting into the time picture with a strong aspect also in July. It is suggested that April, in the application period of the Solar Arc, is going to be very important. It will probably be the month of occurrence.

Where we see such a cluster focus of measurements, the TP -somewhere “in there”-can focus the sense of all the other measurements. We try to find it, and then we can offer our client a specific date of high probability, rather than a general period of a week or month. We draw a TP for some time in April, say, and then we adjust it, maneuvering the date to one of high “trigger-value.” We can see this date as an amalgam of all the other measurements, an averaged reference date, if you will.

As well, a dramatic TP discovered independently from a clustered measurement focus, apparently can also announce a key date. In such a case, further measurement study almost always reveals other measurements of importance occurring simultaneously.

The key signal in TP measurements is when the TP Moon crosses an Angle (or squares it) in the natal chart and/or makes a conjunction, square, or opposition with a key planet. The other TP-planets play a supporting (or background) role to the TP Moon, and their positions can be significant as well. So, a double-ringed chart is used with the TP positions in the outer ring. Orbs are very tight (less than two degrees) and, as in Solar Arcs, only “hard” aspects are observed. [Use the Mean measurements and Solar Arc MC, if given the option.]