Divisional charts

A divisional chart reworks the same planetary positions through a division of each sign. The D9, for example, splits every sign into nine parts. Ascendant derives all of them from the shared Placements, so asking for more divisions costs very little extra and never changes the D1.

This guide shows how to request divisions, read the result, tell divisional charts apart from D1 in your types, and map one longitude on its own.

Supported divisionsCopy Anchor Link

Ascendant supports D1 plus fifteen divisional charts:

The type Chart.Division lists exactly these numbers, so TypeScript rejects any other value at compile time.

Request divisionsCopy Anchor Link

Pass the divisions you want as the second argument to Chart.generate:

import { Chart, Runtime } from "astro-ascendant";
import { DateTime, ManagedRuntime } from "effect";

const runtime = ManagedRuntime.make(Runtime.MainLayer);

const located = Chart.LocatedMoment.make({
  moment: Chart.Moment.make({ date: DateTime.makeUnsafe("2000-01-01T12:00:00Z") }),
  latitude: 12.9716,
  longitude: 77.5946,
});

const calculation = await runtime.runPromise(Chart.generate(located, [9, 10]));

The result's charts always starts with D1, followed by the divisions you asked for. They come back in numeric order with duplicates removed, so [10, 9, 9] gives D1, D9, and D10.

To get every divisional chart at once, list them all:

const everything = [2, 3, 4, 7, 9, 10, 12, 16, 20, 24, 27, 30, 40, 45, 60] as const;
const calculation = await runtime.runPromise(Chart.generate(located, everything));

D1 versus a divisional chartCopy Anchor Link

calculation.charts is typed as a D1 chart followed by any number of divisional charts, so you can split it directly:

const [d1, ...divisional] = calculation.charts;

d1.angles; // chart angles, only on D1
d1.rulingPlanets; // only on D1
d1.houses[1].subLord; // KP lords, only on D1

When you have a Chart.Chart, a value that could be either, check its division to narrow it:

const describe = (chart: Chart.Chart) =>
  chart.division === 1 ? `D1 with ${chart.rulingPlanets.length} ruling planets` : `D${chart.division}`;

The two kinds differ like this:

Divisional charts have no KP data because those belong to source longitudes, and a mapped longitude is not a source longitude. Their houses are whole signs whatever house system you chose.

Read a divisional chartCopy Anchor Link

Each chart has twelve houses, keyed 1 to 12. A divisional house has these fields:

A chart also records its division and its provenance, which for every divisional chart is the Parashari whole-sign-from-mapped-lagna method.

To find where a planet sits, scan the houses. The data is one-directional on purpose: a house lists its planets, but a planet does not carry its house.

const signOf = (chart: Chart.Chart, planet: Chart.Planets) =>
  Object.values(chart.houses).find((house) =>
    house.planets.some((placed) => placed.name === planet),
  )?.sign;

const d9 = calculation.charts.find((chart) => chart.division === 9);
const sunInD9 = d9 && signOf(d9, "Sun"); // "Leo" for the birth above

Example: one birth through every divisionCopy Anchor Link

For the birth above, the Lagna and Sun land in these signs:

The D1 uses the default KP settings, Placidus houses, but the sign of each planet is the same under any house system. The house system changes only D1's cusps.

Map one longitudeCopy Anchor Link

If you need only the divisional position of a single longitude, skip the chart and use getDivisionalTarget:

import { getDivisionalTarget } from "astro-ascendant/chart";
import { Effect } from "effect";

const target = await runtime.runPromise(getDivisionalTarget(256.5924, 9));
// {
//   signIndex: 4,          // 0 = Aries, so 4 = Leo
//   degree: 29.33,         // degree within the target sign
//   longitude: 149.33,     // the mapped longitude
// }

For the Sun at 256.59° in D1, the D9 target is Leo at 29.33°, which matches the Sun's D9 sign in the table above. For division 1, the function returns the source position unchanged. The same function is also exported from astro-ascendant/chart/divisional-mapping.

Where divisions are usedCopy Anchor Link

• Karakamsha reads the D9 sign of each Atmakaraka planet. See Jaimini calculations.
• Parashari readings use divisional charts for the quality of a result, with the Lahiri and whole-sign settings from Choose a school and settings.

When it failsCopy Anchor Link

• An unsupported division number is a compile-time error. If a value gets past the types, for example through a cast, Chart.generate ends in a defect, not a typed failure, so validate numbers from untrusted input before you pass them in.
• Chart.generate fails with a ChartCalculationError at the "houses" stage if the chosen house system's D1 cusps do not divide the circle into twelve houses.
• getDivisionalTarget fails with a DivisionalMappingError when the longitude cannot be used.

See Errors and typed failures for how to handle them.