Panchangam Reference

Provisional Vakya lunar longitude ​

astronomy.vakya-longitudes

A provisional nine-value project offset alters the inherited Surya Siddhanta lunar model.

Assurance ​

LevelCurrent statement
Documented and traceableYes — the canonical record includes the process and a worked example.
Regression or reproduction checkedLinked to 1 repository test file(s).
Independently source-supportedNot independently verified at this level; current behavior is regression-pinned.

Computation method ​

Method type: formula

Choose one of nine project offsets from 3,031-day blocks since the code epoch and add it to the Surya Siddhanta Moon; the Sun remains the Surya Siddhanta Sun.

Process ​

  1. Compute absolute elapsed days K from the Surya Siddhanta code epoch.
  2. Select phase index floor(K / 3031) modulo 9.
  3. Read the corresponding correction from [0, +0.5, +1, +0.5, 0, -0.5, -1, -0.5, 0] degrees.
  4. Add the correction to the Surya Siddhanta Moon and normalize to one revolution.
  5. Subtract the inherited Surya Siddhanta Sun to obtain Vakya elongation.

Formulae ​

Provisional lunar correction ​

text
i = floor(abs(JD - epoch) / 3031) mod 9
M_vakya = (M_SS + correction[i]) mod 360
E_vakya = (M_vakya - S_SS) mod 360
  • i: nine-phase table index
  • M_SS: Surya Siddhanta Moon longitude
  • S_SS: Surya Siddhanta Sun longitude
  • E_vakya: corrected elongation

Worked example ​

Hyderabad sunrise, 2026-06-11 ​

Inputs

  • UT Julian day: 2461202.5077662035
  • Elapsed days from code epoch: 1,872,737.2182337036
  • Surya Siddhanta Moon: 0.5772516191 degrees

Calculation

  1. floor(1,872,737.2182 / 3,031) modulo 9 = 5.
  2. Correction[5] = -0.5 degrees.
  3. Normalize 0.5772516191 - 0.5 and subtract the Surya Siddhanta Sun.

Result

  • Vakya Moon: 0.0772516191 degrees
  • Vakya elongation: 304.4565745224 degrees

Method notes ​

  • This documents current code exactly; the table derivation is unresolved and tracked separately.
  • The 3,031-day block must not be represented as a verified 248-year Vakya cycle.

Contract ​

Owning layer: engine-core
Claim kind: regional-convention
Time basis: Julian day with inherited Surya Siddhanta solar longitude.

Inputs ​

  • Julian day
  • Vakya correction table

Outputs ​

  • corrected lunar longitude
  • corrected Moon-Sun elongation

References and evidence ​

Evidence classes: astronomical, regional_convention, project_heuristic
Verification states: engine_pinned

No registered source derives the nine-value/3,031-day model; issue 176 tracks source reconstruction and possible correction.

vakya.provisional_lunar_model ​

Evidence class: project_heuristic
Verification state: engine_pinned
Locator: _VAKYA_CORRECTIONS and _VAKYA_CYCLE_DAYS; research gap tracked in GitHub issue 176
Last reviewed: 2026-08-27
Scope: The current nine-value offset over 3,031-day steps is regression-pinned but has no registered primary-table derivation or published-Vakya comparison set. It must be described as provisional, not as a verified 248-day or 248-year Vākya algorithm.

Sources ​

  • No external source is registered for this claim.

panchangam.non_drik_engine_outputs ​

Evidence class: astronomical
Verification state: engine_pinned
Locator: tests/test_surya_siddhanta_engine.py and tests/test_vakya_engine.py

Scope: Regression tests preserve the current Surya Siddhanta and Vakya Pancha-Anga and sky-event outputs. No independent published-Panchangam comparison set is registered, so engine-pinned output must not be described as externally verified.

Sources ​

  • No external source is registered for this claim.

The complete machine-readable source registry is available in provenance.json. A regression fixture or same-code reproduction is not independent verification.

Reproduce and review ​

Run the linked tests, then the complete offline contract:

bash
python tools/verify_project.py

Public surfaces ​

  • python-library
  • mcp
  • ics
  • website
  • generated-data

Limitations ​

  • The current model must not be described as a faithful 248-entry lunar-vākya table or as independently verified against a published Vakya Panchangam.

Implementation ​

This route is generated from computations.json. Edit the registry and canonical reference prose in the same pull request as a behavior change.