Solar Arc vs Secondary Progression: Which Systems to Use?
Secondary progression (i.e. “a day for a year” method of directing a natal chart) has been around for a long time, but it was by no means the only method of progressing a horoscope. Throughout the history of astrology, astrologers have invented different methods of projecting a natal chart into the future.
Right now, Solar Arc and Secondary Progression are the most popular methods used by professional astrologers. Noel Tyl popularized the Solar Arc method (although he still uses Secondary Progressed Moon). There are many fine astrologers using Secondary Progression as their tool of choice, so both methods are here to stay.
Difference between Secondary Progressed and Solar Arc Planets
One of the key differences between the two methods is that in Solar Arc you get to advance the slower moving planets (Saturn through Pluto) that hardly move in the Secondary Progression method, so this tends to add more interpretive possibilities when forecasting.
Noel Tyl, who has written extensively about both progression methods, stated that in our modern era, important life changes (e.g. divorce, job change, relocation, etc) occur much more frequently than in previous times – thus we need a method that more accurately reflects the rapid pace of modern life.
In Secondary Progression, outer planets are pretty much unusable due to how slowly they move. In Solar Arc, you’ll see natal outer planets located in cadent (3rd, 6th, 9th or 12th) houses crossing an angle within the first 10-30 years of life, frequently representing major restructuring of family unit, home environment, or the profession.
How to Calculate Solar Arc Planets’ Movement
Solar Arc planets “move” at the speed of Secondary Progressed Sun, which is approximately one degree per year. If you obtain the current location of SP (secondary progressed) Sun, and calculate the arc (angular distance) between the SP Sun and the natal Sun, you have the “Solar Arc” you need to progress your natal chart to its current Solar Arc position (your astrology software will make this calculation for you automatically.)
Even a fast-moving planet like Venus will have a longer time frame (say 6 months applying, and 3 months separating) to be in orb using a Solar Arc method: this means Solar Arc of Venus aspecting the natal Sun (written Venus=Sun) would last for about 9 months, strongly suggesting the success of a relationship or an artistic endeavor.
In transit, Venus moves so fast that it can’t have much of an impact except for a couple days of pleasantness. Similar things can be said of Jupiter, whose transit is fleeting but under the Solar Arc, suggests a 9 months period in which reward or opportunity is likely to be presented.
Testing Solar Arc in Your Own Horoscope
Solar Arc is relatively easy to test in your own horoscope: add 1 degree per year to the natal planets to see how they move and form an aspect with the natal planet. The orb needs to be exact (less than one degree) in order for the Arc to be in effect, and we count hard aspects (conjunction, square and opposition) only.
If natal ASC (Ascendant) is at 12 Leo, and natal Saturn is at 22 Leo, this means Solar Arc ASC will conjoin natal Saturn at age 10 (we write ASC=Sat to denote this period), then we ask if there had been a status change within the family around that age: some Saturnian event such as death in the family, sickness, move, or change in father’s position, etc.
Conclusion: Secondary Progression vs Solar Arc?
Solar Arc is a modern derivative of Secondary Progression that allows the astrologers to utilize Saturn and outer planets more fully in their predictive work. Many modern astrologers including myself use Solar Arc (which gives central importance to the Secondary Progressed Sun’s movement) in combination with Secondary Progressed Moon (which is a very important timer of life progress.)
To study further, you can read the article on Solar Arc Interpretation.
A Must Read Reference: Solar Arcs by Noel Tyl
Noel Tyl has written extensively about his method of prediction in Solar Arcs: Astrology’s most successful predictive system. The book is actually a summary of his predictive method incorporating transits, Solar Arcs, Secondary Progressed Moon, as well as Tertiary Progressed Moon.