Sources & Calculation Methodology
A transparent technical explanation of the astronomical algorithms and scriptural standards powering this platform.
1. Astronomical Ephemeris Engine
All celestial positions (Sun, Moon, Mercury, Venus, Mars, Jupiter, Saturn, and Lunar Nodes) are computed via the browser-compatible VSOP87 planetary theory and NOVAS C 3.1 celestial mechanics algorithms implemented in the open-source astronomy-engine library (licensed under the MIT License).
2. Ayanamsha Selection (Lahiri / Chitrapaksha)
To convert Tropical (Sayana) ecliptic longitudes to Sidereal (Nirayana) coordinates used in Vedic astrology, we adhere strictly to the Lahiri (Chitrapaksha) Ayanamsha:
- Epoch Reference: J2000.0 (January 1, 2000, 12:00 TT) baseline of 23° 51' 25.53" (23.85709°).
- Precession Rate: General precession in longitude modeled dynamically via the IAU-standard polynomial rate of approximately 50.29 arcseconds per Julian century.
3. Topocentric Solar & Lunar Rise/Set Conventions
Sunrise and sunset are calculated for the topocentric position of the observer on Earth's surface:
- Atmospheric Refraction: Calibrated with the standard 34 arcminutes (0.5667°) refraction at sea level.
- Solar Semi-Diameter: 16 arcminutes (0.2667°).
- Zenith Angle: The geometric center of the Sun is at 90° 50' from the local zenith when the upper limb touches the horizon.
4. The Five Limbs (Panchang) Formulas
- Tithi: Determined by (Moon Longitude − Sun Longitude) / 12°.
- Nakshatra: Determined by Moon's Nirayana longitude divided into 27 equal segments of 13° 20' (13.3333°).
- Yoga: (Moon Nirayana Longitude + Sun Nirayana Longitude) / 13° 20'.
- Karana: Half-tithi intervals of 6° (60 total per lunar month).
- Daytime Divisions (Choghadiya & Rahu Kaal): Exact local duration between sunrise and sunset divided into 8 equal parts (Yama) and daytime divided into 15 equal parts for Abhijit Muhurat.
5. Scriptural & Traditional References
Religious interpretations and ritual guidelines are drawn from respected public-domain classical authorities:
- Surya Siddhanta (Classical astronomical treatise)
- Brihat Samhita and Brihat Parashara Hora Shastra
- Nirnaya Sindhu and Dharma Sindhu (Foundational manuals for festival timing)
- Publications of the Calendar Reform Committee (Government of India)