Arabic parts (lots)
An Arabic part — older usage calls them lots, which is the more accurate translation — is a point computed by adding two chart positions and subtracting a third, projected from the Ascendant. The Lot of Fortune (Ascendant + Moon − Sun by day; Ascendant + Sun − Moon by night) is the most-used; the tradition catalogues dozens. Each lot foregrounds a particular life theme by combining the right ingredients.
The formula
Every lot is a triangle. Pick three chart positions A, B, C; the lot is at longitude (A + B − C), reduced to the [0°, 360°) range, and it inherits the sign and house of that longitude. The Lot of Fortune uses Ascendant, Moon, Sun (day) or Ascendant, Sun, Moon (night) — the formula reverses by sect, which is true for many but not all of the classical lots.
Reading a lot
A lot is a degree, not a planet, so it has no rulership of its own. To read it, find the planet ruling the sign it falls in (its lord) and the planets aspecting it. The Lot of Fortune in Cancer in the 5th house, with the Moon in the 10th, is read through the 10th-house Moon as the Lot's lord. A lot conjunct a benefic with no afflictions is well-placed; a lot conjunct a malefic in a debilitated sign is afflicted.
Beyond Fortune
Hellenistic practice uses many lots. The Lot of Spirit (the day/night reverse of Fortune) signifies action and intention. The Lot of Eros is constructed from Spirit and Venus; the Lot of Necessity from Fortune and Mercury; the Lot of Courage from Mars; and so on. Vettius Valens catalogues a large set in Book IV. Each is a lens — useful for the theme it highlights, redundant for any other.
How Netra uses it
The Lots view computes the Lot of Fortune and the Lot of Spirit by default and offers a custom-formula editor (since v2.17.0) so any classical or homegrown lot can be added by typing its addition rule. The lord and aspects of each lot are surfaced inline.
Illustrative natal chart — the technique above applies to any chart you compute in Netra.
Sources
- Vettius Valens, Anthology, Book IV
- Manilius, Astronomica, Book III
- Al-Biruni (R. Ramsay Wright trans., terminology only)
See Sources for the full corpus and the public-domain policy.
Related
- Essential dignities — The five-fold table of planetary strength by zodiacal placement — domicile, exaltation, triplicity, term, and face.
- Sect — The diurnal–nocturnal split that determines which planets are in their preferred environment.
- Midpoints — The half-sum point between two planets — a sensitive degree where their themes meet and a third body can activate them.
- Antiscia and contra-antiscia — Solstice-axis reflections — a hidden contact line that runs through every chart.