Accuracy
panchang-ts · v5.0.0 · MIT
What the 8,368-test suite verifies against reference panchangs, end-time drift bounds, ayanamsa provenance, and documented festival-dating tradeoffs.
8,368 tests across 121 files, including fixtures cross-verified against reference panchang calculations spanning 2025–2026 across 10 Indian cities plus New York, London, Sydney, Dubai, and Singapore (the diaspora fixtures cover DST on America/New_York).
What is verified, and to what tolerance
| Element | Accuracy |
|---|---|
| Sunrise / Sunset | ≤29 s observed vs reference minute-midpoint (±45 s tolerance) |
| Moonrise / Moonset | Meeus apparent-upper-limb (refraction + parallax); ~3–5 min vs simpler-horizon authorities is expected |
| Tithi / Nakshatra / Yoga / Karana names | exact match vs reference |
| Tithi / Nakshatra / Yoga / Karana end-times | ≤60 s vs Drik across all 20 audited comparisons (tithi 46 s, karana 51 s, nakshatra 24 s, yoga 60 s) |
| Ayanamsa (Lahiri) | reproduces DrikPanchang’s published value to ~0.01″ across 1950–2050 |
| Planetary positions (Sun–Saturn) | ±0.02° sidereal |
| Planetary positions (Rahu/Ketu, mean node) | ≤0.5° typical; ±2° tolerance |
| Planetary positions (Rahu/Ketu, true node) | ≤0.6° typical (Meeus periodic correction) |
| Lagna sidereal longitude | cross-checked against Jagannath Hora reference charts |
| D1 / D9 house placement | exact match vs reference for 9-graha placement |
| Ashtakoot total | ±1 point per pair across 30+ matched pairs |
| Sade Sati arc start/end | ±1–2 days vs authoritative ephemerides |
Detection conventions
| Element | Convention |
|---|---|
| Aadal / Vidaal | classical Moon-from-Sun nakshatra-distance rule (AstroShastra, HoraSarvam, Ernst Wilhelm) — NOT the Tamil-Vakya weekday rule used by some online panchangs |
| Varjyam | emits the sunrise-anchored nakshatra’s window only |
| Do Ghati Muhurta | does not rotate by weekday — the same 30-name deity-keyed sequence applies every day |
Festival detection — documented tradeoff
The library uses tithi-at-sunrise to resolve a festival to a calendar day. Some authorities use other classical rules for certain festivals; where those rules pick a different day, output can drift ±1 day:
| Alternative rule | Affects |
|---|---|
| Tithi-at-midnight | Krishna Janmashtami, Maha Shivaratri, Diwali / Lakshmi Puja |
| Madhyahna-vyapini | Ganesh Chaturthi (edge years), Akshaya Tritiya 2026 |
| Kshaya-tithi handling | Ugadi 2026-03-19 (Pratipada is Kshaya) |
Everything else — Holi, Ugadi (non-Kshaya years), Rama Navami, Raksha Bandhan, Ganesh Chaturthi (normal years), Navaratri, Dussehra, Karva Chauth, Hanuman Jayanti — matches the canonical date across the 2025 and 2026 fixtures. See also Festivals.