Progressed Charts

Mean Progressions

A progressed chart for a particular date is calculated by determining the time elapsed since the birth or event chart, and applying a progression rate to the elapsed time to get a progressed elapsed time, and then adding that progressed elapsed time to the birth or event chart date. For example, secondary progressions are based on a correspondence of one year to one day. Therefore a progressed chart for a time and date 32.745 years after the birth time and date is calculated as a natal chart would be for a time and date 32.745 days after the birth time and date.

Once the planetary positions are determined in this manner, the progressed Midheaven is calculated according to the currently selected method of angles progression, and then the other chart angles are derived from the Midheaven according to the chart’s location.

True Progressions

Instead of using a progression rate determined from mean periods, it is possible to base the progression calculation upon true (fluctuating) periods. This is of practical use with progression rates that are based on the moon’s cycles, because the moon’s cycles do fluctuate significantly with time. Solar Fire offers this option in relation to the tertiary progressions of fixed charts (but not in the dynamic module). In this case one is assuming that each true lunar cycle corresponds to one day in the progressed chart, so the calculation involves finding the exact times of the lunar returns before and after the target date, and interpolating between these to find the exact fractional lunar cycle to add to the number of completed lunar cycles at the target date. The resulting number of lunar cycles is the number of days by which to progress the chart.