Ayanam and Rituvu

panchangam.ayanam-rituvu

Solar position classifies the half-year and six seasonal names.

Assurance

Level	Current statement
Documented and traceable	Yes — the canonical record includes the process and a worked example.
Regression or reproduction checked	Linked to 1 repository test file(s).
Independently source-supported	Not recorded as independently verified. The disclosed provenance state remains authoritative.

Computation method

Method type: decision-table

Ayanam uses the engine's sidereal solar sign at sunrise, while Rituvu independently bins the shared tropical Swiss solar longitude into a twelve-sign-to-six-season lookup.

Process

1. Compute the sidereal sunrise Sun sign index from the selected engine.
2. Return Uttarayanam for sign indices 9, 10, 11, 0, 1, or 2; otherwise return Dakshinayanam.
3. Compute tropical Swiss Sun longitude at the same sunrise instant.
4. Take floor(tropical longitude / 30) modulo 12 and use that index in RITUVU_NAMES.

Worked example

Hyderabad, 2026-06-11

Inputs

• Drik sidereal Sun: 55.889366 degrees
• Sidereal sign index: floor(55.889366 / 30) = 1
• Tropical solar sign maps to the Grishma entries

Calculation

1. Index 1 is in the Uttarayanam set.
2. The tropical-sign lookup is evaluated separately from the sidereal sign.

Result

• Ayanam: Uttarayanam
• Rituvu: Grishma

Method notes

• This hybrid is intentional: Rituvu does not use the selected engine's sidereal Sun.
• Criterion-level source locators for the naming convention remain unresolved.

Contract

Owning layer: engine-core
Claim kind: regional-convention
Time basis: Solar position at sunrise.

Inputs

• solar sign or tropical solar longitude

Outputs

• Ayanam
• Rituvu

References and evidence

Evidence classes: textual, regional_convention
Verification states: needs_locator

Calendar semantics need more exact source locators.

panchangam.calendar_semantics

Evidence class: textual
Verification state: needs_locator
Locator: No precise locator is registered.

Scope: Samvatsara, Ayana, Ritu, lunar-month, Paksha, weekday and Rasi labels combine astronomical calculations with calendar rollover conventions. They require criterion-level locators and regional-scope notes; astronomical correctness alone does not verify the naming convention.

Sources

• Muhurtha (Electional Astrology) — B. V. Raman; UBS Publishers' Distributors, 1993, ISBN 9788185674681, 181 catalogued pages; authority type: modern_synthesis

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

• tests/test_drik_engine.py

Run the linked tests, then the complete offline contract:

python tools/verify_project.py

Public surfaces

• python-library
• mcp
• ics
• website

Limitations

• Rituvu uses tropical solar longitude while other fields are predominantly sidereal.

Implementation

• owner: telugu_panchangam/engines/base.py — ayanam_name
• owner: telugu_panchangam/engines/base.py — rituvu_name

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