There is a disagreement in the literature about the best way to calculate solar returns. Should we have the Sun return to its birth position with respect to the vernal point or with respect to the fixed stars? Should charts cast in the tropical zodiac be “corrected” for precession of the equinoxes? Should charts cast in the sidereal zodiac be “corrected” so that the natal sun returns to its position with respect to the vernal point?
As an aside, let us note that the solar return was traditionally cast for the birth place, and this practice was in effect until Morinus in the 17th century tried to make astrology look more scientific by ridding it of all traces of divination. He thus insisted that the planets can only exert their measurable objective forces at the location of the native at the moment of the solar return and that any type of symbolic “influence” (profections, lots, symbolic directions, firdaria and other time-lord techniques, etc.) was superstitious nonsense. Unfortunately, Morinus seems to have thrown out the baby with the bathwater.
The earliest “solar returns” of Hellenistic times were most likely the transiting planets to the birth chart on the day that the sun was observed to be at its natal position in the heavens. I’m not sure what type of instruments the ancients used to measure the position of the sun, but if they relied on shadows cast by the sun, then they were using the tropical year as a basis for measurement. For example, as explained at the site Windows to the Universe (italics mine): “In 240 B.C., the Greek astronomer Erathosthenes made the first good measurement of the size of Earth. By noting the angles of shadows in two cities on the Summer Solstice, and by performing the right calculations using his knowledge of geometry and the distance between the cities, Eratosthenes was able to make a remarkably accurate calculation of the circumference of Earth.”
In his notes about Abu Ma’Shar’s On the Revolutions of the Years of Nativities, translator and astrologer Benjamin Dykes comments that Abu Ma’Shar calculates solar returns using the tropical year as defined by Ptolemy (quoting Hipparchus) of 365.24667 days per year. The current value of the tropical year is 365.24219 days. Thus, Abu Ma’Shar’s tropical year was a little longer than the current value by about 6.45 minutes of time. In Ma’Shar’s mundane work, however, he followed the sidereal model of earlier astrologers like Masha’allah and the Persians, and used 365.259 days (or 365.2590278 days, as Masha’allah had it), while our modern sidereal year is 365.256363 days.” In short, Abu Ma’Shar used the topical year for solar returns but the sidereal year for mundane charts. Note that one can use the tropical year for timing in a chart cast in the sidereal zodiac. In fact, many Hindu astrologers time the activation of their various dasas (a sidereal technique) in terms of the tropical year of 365.24219 days.
Interestingly, but not surprisingly, the Hindu astrologers who learned about solar returns from the Persians apparently also followed this practice of using the tropical year for measuring when the Sun would return to its natal position. To quote from the distinguished scholar P.V.R. Narashima Rao in his essay Redefining Tajaka Varshaphal Charts: “In the teachings of Maharshi Parasara to Maitreya in ‘Vishnu Purana’ chapter 2.8. Maharshi Pararsara taught Maitreya that a solar year consists of 2 ayanas and that each ayana consists of 3 ritus (seasons). This link to seasons clearly points to tropical zodiac. A solar year based on tropical zodiac (i.e. the time Sun takes to complete exactly one rotation around the tropical zodiac) is tied to seasons. … If we take the sidereal zodiac, it is not tied to seasons” (italics mine).
The above quote from Parashara is similar to what Abu Ma’Shar writes in his first chapter about solar returns (p. 53, Dykes translation, 2010): “… the year is divived into four seasons … These seasons being completed, the year is restored to its first disposition …” In other words, a return of the sun to its “first disposition” or natal position occurs in the length of exactly four seasons, which is the measurement of the topical year.
P.V.R. Rao draws the following conclusions from the teachings of Maharashi Parasara cited above and the choice of tropical versus sidereal years:
Rao concludes that “both tropical and sidereal zodiacs are needed:
• Sidereal zodiac: Used for all matters related to space, i.e. definition of rasi chart and divisional charts
• Tropical zodiac: Used for all matters related to time, i.e. definition of months, seasons, ayanas and years.
• Tajaka varshaphal chart is cast every year when Sun is exactly at the same tropical longitude as at birth.” (bold mine)
In other words, according to the the classic Hindu text and teachings of Parashara, because the solar return is a time-based technique, it depends on the tropical zodiac for measurement. The implication for Hindu astrologers is that they should calculate the sun’s return to its tropical position in the birth chart. Most Western astrologers, following the teachings of Abu Ma’Shar, already measure the sun’s return in the tropical zodiac. Nonetheless, some Western astrologers advocate “correcting for precession” but this method lacks support in the traditional literature which calculated the return of the sun to its birth position in the tropical zodiac.
Regarding the idea of using the tropical return in an otherwise sidereal chart, my practice has been to use the sidereal year with the sidereal zodiac to calculate the sun’s return. Generally the use of the sidereal solar return with sidereal zodiac charts has been an effective predictive technique. I have not yet experimented with using the tropical return of the sun in sidereal charts.