Recently, Wade Caves gave an excellent presentation for the Skyscript Member Group about the Part of Fortune in which he discussed the history of this “lot” and whether its inventor intended the longitudes of the Sun and the Moon to be reversed when calculating it, according to the sect of the chart, that is, during the day (Asc + Moon – Sun) vs. during the night (Asc + Sun – Moon). According to documented history, this has been a point of controversey since at least the 1st century CE. Links to Wade’s video and article are:

Read the article: https://www.skyscript.co.uk/fortuna.html

Watch the recording: https://www.youtube.com/watch?v=OEjwYV0jj_c&t=269s

A discussion area has also been set up in the Skyscript forum for anyone who’d like to comment at: https://www.skyscript.co.uk/forums/viewtopic.php?p=133786

The fundamental formula of the Part (Lot) of Fortune by day is: Asc + Moon – Sun, which means that you measure the arc along the ecliptic, starting from the Sun and ending at the Moon, and then in a day chart you project that Sun-to-Moon arc from the Ascendant to arrive a point called the Part of Fortune. In essense, if you were to place the Sun on the Ascendant degree, the Part of Fortune would then fall on the Moon, which is to say that the angle from the Sun to the Moon is the same as the angle from the Asc to the Part of Fortune (Sun ==> Moon equals Asc ==> Fortuna) or, put another way, the Sun is to the Asc as the Moon is to the Part of Fortune. In fact, in Tetrabiblos Book III, Chapter 10 (in some editions III.11), Ptolemy describes the Part of Fortune (Lot of Fortune/τύχη) as functioning like “the horoskopos of the Moon” — essentially treating it as if it were the Moon’s own ascendant.

Wade’s basic argument is that Ptolemy’s understanding is indeed the basic definition of the Part of Fortune, and therefore no reversal by night of the longitudes of the Lights is indicated. The Lot of Fortune at all times, by day or by night, functions like the horoskopos [Ascendant] of the Moon. William Lilly agreed with Ptolemy and used only the “day formula” in his own practice of astrology. Wade points out that the texts of ancient astrologers who reverse the formula in night charts “are missing a compelling rationale as to why we are adding and subtracting longitudes between luminaries and the ascendant.”

How is it then that some early Hellenistic astrologers reversed the formula of the Part of Fortune in night charts? One possibility is that they misunderstood the original definition which may date back to the legendary writings of Nechepso and Pitosoris, no longer extant. Another possibility is that two distinct traditions developed regarding the Lot of Fortune, one that used only the day formula and another that varied the formula based on the sect of the chart.

Evidence reveals that the controversy goes back to at least the first century CE. Wade cites chart No.81 from the book Greek Horoscopes (Neugebauer and van Hoesen). This chart is recorded on P. Lond. 130, a papyrus from the Greek Papyri in the British Museum collection. The author of this papyrus is unknown, but it dates back to the year 81 CE — a century earlier than Vettius Valens or Claudius Ptolemy. Given the content and educated literary style of the text on this papyrus, it is possible that the astrologer was familiar with the work of the first century scholar and astrologer Balbillus the Wise, high priest at the Temple of Hermes in Alexandria.

In this nocturnal chart the Part of Fortune is calculated to lie in Sagittarius, and the author adds superciliously that only an ignorant astrologer would place Fortuna in Libra (the result obtained with the “night formula’). This anonymous astrologer sounds arrogant but well educated, and is rather disdainful of more poorly informed astrologers who follow the mistaken tradition of reversing the formula in night charts. In the following century Ptolemy commented that the only way to calculate the Part of Fortune was his way: take the arc from, the Sun to the Moon and project it from the eastern horizon (Asc + Moon – Sun). Ptolemy also criticized the earlier method of timing circumambulations by ascensional times around the zodiac wheel was overly simplistic, uninformed and scientifcally invalid. Here is a modern approximation of chart No.81:

Note the symmetry around the horizon of the Part of Fortune and the Part of Spirit (the nighttime Part of Fortune in this chart). The reversal of the Sun and Moon in the daytime Part of Fortune formula gives as a result the position of the Part of Spirit or Daimon. The midpoint of Spirit and Fortune is always the horizon. It may be that a tradition existed which emphasized the importance of symmetry in astrology and therefore posited a day and a night Part of Fortune based on the sect of the chart. We see such symmetry in the Thema Mundi, which is a foundational concept for much of Hellenistic astrology.

Consider the following rough approximation of the famous Thema Mundi chart for the creation of the world:

Astrologers impressed with Euclidean mathematics and the symmetry of the Thema Mundi could reasonably argue in favor of the “nighttime formula” for the Part of Fortune as a good symbol of material good fortune at the very beginning of the universe. A more spiritually-minded astrologer, like Vetius Vallens, might prefer splitting the Part of Fortune into Fortuna and Spirit, whereas a natural scientist, like Ptolemy, might prefer a single formula that can be used to determine length of life more easily.