Solar Arcs
Solar Arc methodology appears to be simple -- it is in its concept, but it has subtleties that are not directly part of other predictive methods. A solar arc can be mathematically determined in several ways, all of which appear to be quite close in their results.
** One could determine the solar arc for their current/prior birthdate by using the Sun's position in the ephemeris for their birth date (either Noon or Midnight will do), then counting forward for the number of days equal to your years for the last birthday party you had. This will give you a solar arc. You advance every component in your chart by this value and then see what aspects and contacts occur between natal and solar arc progressed planets.
** Or you could cast your natal chart and a chart for "X" number of days later to get the difference in Sun travel distance. As above, add this value to every natal positional value to get your solar arc progression (it is actually called a "direction" and not a progression as it directs everything forward the same amount).
** Or you could use your Astrological program of choice, and choose one of several methods of Solar Arc advancement, each with its own small differences in terms of results.
Now, most astrologers who use Solar Arc methodology know that they can proportionalize the small amount of daily advance by the Sun to get a result applicable to a given day or week within the year.
Also, most astrologers who use Solar Arc methodology use the 90 degree wheel that was popularized by R. Ebertin for use with his classical book on midpoints, the Combination of Stellar Influences. As I have said many times, no astrologer is without this book and no student should study astrology without having this book at hand. The 90 degree wheel was developed as a chart form in which the circular chart is divided by 90 degrees, not 360 degrees. This results in every cardinal sign being laid over each other such that the first third of the circle represents Aries, Cancer, Libra and Capricorn. The next third of the chart represents Taurus, Leo, Scorpio and Aquarius, while the last third represents Gemini, Virgo, Sagittarius, and Pisces.
This type of chart provides plenty of space for marking the position of the planets very clearly and precisely. This is important because a clear plastic overlay is used which has a prominent arrow with degree markings noted that spread to both the right and the left increasingly from the arrow. Turning the arrow to any natal or solar arc directed chart component permits the eye to see which other planets are equidistant from the arrow or the planet that it is pointing toward.
Now, comes the role of the book, Combination of Stellar Influences, or CoSI. It defines the interpretive meaning for any pair of planets with another planet or chart angle at its midpoint. These book statements are quite precise and are often shockingly true although they are best "adjusted" to fit the many situations or life-contexts that are part of your everyday life.
As a predictive tool, the timing that they represent is often representative of a one or two week period. As Minderwiz pointed out, Noel Tyl has a book out that specifically addresses this methodology although many of his other books also address this methodology. Note also that Ebertin, the developer of this system as we now know it, has several books out on this method as well. They offer spectacular examples covering all walks of life. I learned this method when I was two months into studying astrology and immediately loved its clarity and application. It is rare to find other predictive systems that are as effective.
Dave