Methodology

This page describes, in technical detail, how every panchang element, muhurat, choghadiya, planetary position and astrological calculator on this site is derived from mathematical astronomical formulas. Our goal is transparency — readers can independently verify the methodology and understand the bounds of the results.

✦ Astronomical Foundation

Every panchang element on this site — sunrise, sunset, tithi, nakshatra, yoga, karana, planetary positions, Rahu Kaal and choghadiya — is derived from mathematical astronomical formulas. We follow the methodology described in Jean Meeus's "Astronomical Algorithms" (Willmann-Bell, 1998, second edition), a widely cited reference that distils the VSOP87 planetary theory and ELP-2000/82 lunar theory into compact, high-precision formulas.

For solar position we use 36 prime perturbation terms which, after accounting for planetary gravitational effects, yield the Sun's tropical longitude to about 0.01°. For lunar position we apply the 38 perturbation terms tabulated by Meeus, giving an accuracy of about 10″ (0.003°).

For tropical-to-sidereal conversion we use the Lahiri (Chitrapaksha) Ayanamsa — the standard adopted in 1955 by the Government of India's Calendar Reform Committee (chaired by Prof. Meghnad Saha). For the year 2026 the Lahiri Ayanamsa is approximately 24°15′. The value increases by roughly 50.3″ per year.

✦ Sunrise and Sunset

Sunrise/sunset computation accounts for three subtleties: (i) atmospheric refraction — the Sun appears about 34′ higher near the horizon than its true position; (ii) the apparent radius of the solar disc, 16′; and (iii) Earth's elliptical orbit and axial tilt. The combined "sunrise depression" is roughly 50′ below the geometric horizon — the moment when the upper limb of the Sun emerges.

Coordinates for 200+ Indian cities are sourced from the IANA timezone database and Geonames. Latitude and longitude are stored to three decimal places, giving sunrise accuracy of ±20–30 seconds. Comparison with established classical almanacs (Drikpanchang, Kalnirnay) usually agrees within ±2 minutes.

Regional variation matters: between Delhi (28.6°N) and Chennai (13.1°N) sunrise can differ by 30–35 minutes in summer. That is why Rahu Kaal and choghadiya for a single date fall at different clock times across cities.

✦ Tithi Calculation

Tithi is based on the angular separation between the sidereal longitudes of Sun and Moon. Formally: tithi-number = ⌊(Moon-longitude − Sun-longitude) mod 360° / 12°⌋ + 1. Shukla paksha runs 1–15, Krishna paksha 1–15 (often shown as 16–30). Average tithi length is 23 h 37 m, but due to lunar orbital ellipticity actual length varies between 19 and 26 hours.

Following the established Indian convention, we use uday-tithi — the tithi prevailing at local sunrise — as the primary tithi for the day. When two tithis fall within a single day, both intervals are shown explicitly.

Compared with established almanacs, tithi-end timings differ typically within 1–3 minutes. The small variance arises mainly from the number of lunar perturbation terms used (we use 38; some almanacs use 23) and ayanamsa subtleties.

✦ Nakshatra, Yoga, Karana

Nakshatra is derived by partitioning the Moon's sidereal longitude into 27 segments of 360° / 27 = 13°20′. Each nakshatra is further divided into four padas of 3°20′ each. In traditional newborn naming, the first syllable is chosen by the pada within the birth nakshatra.

Yoga is based on the sum of the sidereal longitudes of Sun and Moon (not the difference, which would be tithi). Yoga-number = ⌊(Sun-longitude + Moon-longitude) mod 360° / 13°20′⌋ + 1. There are 27 yogas, each lasting approximately 24 hours on average.

Karana is half of a tithi — each tithi contains two karanas. Eleven karana names cycle: seven movable (Bava, Balava, Kaulava, Taitila, Gara, Vanija, Vishti) and four fixed (Shakuni, Chatushpada, Naga, Kimstughna). Vishti karana (also called Bhadra) is traditionally regarded as inauspicious.

✦ Choghadiya and Rahu Kaal

Choghadiya is computed by dividing the day-period and night-period into eight equal segments each. Day = sunrise to sunset; night = sunset to next sunrise. Each choghadiya = total period / 8, so the length varies with day length. In summer a day-choghadiya runs about 90 minutes; in winter about 75 minutes.

The ruling planet of each choghadiya cycles by weekday. Choghadiyas ruled by benefic planets (Venus, Moon, Mercury, Jupiter) are called Amrit / Shubh / Labh; those ruled by malefics (Saturn, Mars, Sun) are Rog / Kaal / Udveg. Char choghadiya is traditionally suitable for travel.

Rahu Kaal follows the same principle — the day is divided into 8 segments, with one fixed slot (~1.5 hours) assigned to Rahu by weekday: Sunday 8th, Monday 2nd, Tuesday 7th, Wednesday 5th, Thursday 6th, Friday 4th, Saturday 3rd. Because this is sunrise-based, Rahu Kaal clock times vary by city.

✦ Accuracy and Limitations

Mathematical precision vs. traditional consensus: our calculations are mathematically high-precision via Meeus, but pinning down a single "correct" tithi is constrained by traditional disagreements between almanacs — some use Lahiri Ayanamsa, others Raman, others Krishnamurti. We use only Lahiri.

What we do NOT compute: full personal kundali analysis, mahadasha/antardasha interpretive predictions, individual marital matching judgments, or any form of "fortune telling". Those are appropriate only in a personal consultation with a qualified jyotishi who can read the full birth chart.

Known limitations: we do not compute the exact local visibility bounds of solar/lunar eclipses — only the global mid-eclipse time (UT). For transits, we cap at secondary perturbation terms. If you ever find a panchang element on this site differing from a trusted classical almanac by 5+ minutes, please write to us.

✦ Editorial Process

Article content on this site is compiled from publicly available classical Sanskrit texts — Surya Siddhanta, Brihat Parashara Hora Shastra, Muhurta Chintamani, Brihat Samhita, Phaladeepika — and standard reference works on Hindu calendrics. We do not publish direct translations of the primary texts; only plain-language introductions to the underlying principles.

We make no personal-review claims by any "expert" or "pandit". The site is run by an editorial team. Readers who notice factual errors are encouraged to email us — corrections are typically made within seven days of verification.

This site is published for educational and cultural reference only. It is not a substitute for personal consultation with a qualified pandit or jyotishi. For decisions concerning marriage, housewarming, health, medical or financial matters, please consult an appropriate domain expert.

✦ References

• 📖 Astronomical Algorithms — Jean Meeus, Willmann-Bell, 1998 (2nd ed.)
• 📖 Surya Siddhanta — classical Sanskrit astronomical text (~5th century CE), translated by E. Burgess (1860)
• 📖 Brihat Parashara Hora Shastra — Maharishi Parashara, foundational text on Vedic astrology
• 📖 Muhurta Chintamani — Ram Daivajna, 16th-century treatise on muhurat selection
• 📖 Indian Calendric System — Calendar Reform Committee Report, Government of India, 1955
• 📖 VSOP87 / ELP-2000 — modern planetary and lunar theories (Bureau des Longitudes, France)
• 🌐 IANA Time Zone Database — for city coordinates and DST handling