Rate for Primary Directions

When primary directions are calculated in a Dynamic report or in a Page object, there are several different methods of determining the exact rate of direction. The Primary Direction rate is always about one year of life per degree of directed arc, but in the "Preferences" dialog, "Progs/Dirns" tab any of the following options may be selected...

•(Ptolemy) 1 Year per Degree - The progression rate is exactly one degree of arc for each year of life.

•Naibod (1 Year for 59’08’’) - The progression rate is 59’08’’ of arc for each year of life, which is the average amount that the sun moves in a day  (360 degrees / 365.242 days in a year).

•Cardan (1 year per 59'12") - The progression rate is 59’12” of arc for each year of life.

•Kepler - Natal Solar Rate in RA - The amount that the sun moves in Right Ascension on the actual day of birth is computed; the progression rate is then this amount for each year of life (also known as Brahe’s key.)

•Natal Solar Rate in Longitude - Similar to Kepler’s key, only computed based on the sun’s motion in Longitude on the day of birth.

•Placidus - True Solar Arc in RA - This is different from the others in that it’s not a fixed rate per year; instead, for a given arc of direction, we find how many days it takes the sun to travel that arc (in right ascension) after the moment of birth; that number of days is then used as the number of years.

•Rate for User Directions - The progression rate is the value set in the “Rate for User Directions” (in this same preferences dialog) per year of life.

Any dynamic reports or page objects which use Primary Directions that are subsequently calculated or displayed will use the newly selected calculation method.

In addition in a Dynamic Report you can opt to have dynamic positions calculated in converse. Prior to Solar Fire 9 all such calculations were based on the Modern method of conversing points, but now you have a choice (see Primary Directions in Solar Fire). You can choose between...

•Classical Converse

This sets Primary Directions to compute converse according to the classical technique, where the direction of a point A to some point B behind it (in converse motion) in computed in exactly the same fashion as the direction of point B to point A in direct motion, and results in the same arc and timing.

•Modern Converse

This sets Primary Directions to compute converses according to a more recent technique, pioneered in the 19th century, where the direction of a point A to some point B behind it is computed using the usual equations, as though A were to move backwards in the sky to B, producing a negative arc; this arc is then flipped to positive before converting to a date.  (Generally this is a different number from the direct motion of B to A.)