Jyotish Ganita
Jyotish Ganita tests the astronomical calculations behind panchanga and chart casting: tithi, vara, nakshatra, yoga, karana, ayanamsa and time conversion. The exam rewards correct formulas and clear assumptions, not memorized almanac values.
Panchanga elements
Tithi is the Moon–Sun elongation divided by 12°; there are 30 tithis. Yoga is the sum of the Sun’s and Moon’s sidereal longitudes divided by 13°20′, giving 27 yogas. Karana is half a tithi. Vara is the weekday, and nakshatra is the Moon’s lunar mansion. Ayanamsa is the precession offset between tropical and sidereal longitudes; Lahiri or Chitrapaksha is widely used in India, while Raman, KP and Yukteshwar differ. Precession is about 50.3 arcseconds per year.
Worked example
Sun at 10° Aries and Moon at 25° Aries give an elongation of 15°. The first tithi covers 0°–12° and the second covers 12°–24°, so 15° is Shukla Dwitiya. The sum of longitudes is 35°, and 35° divided by 13°20′ is 2.625, which falls in the third yoga. In the standard karana sequence, the first half of the second tithi is Bava. The answer must state that these are sidereal longitudes.
Traps
- Using tropical longitudes without ayanamsa.
- Treating tithi as a fixed 24-hour day; tithis vary in length.
- Confusing yoga with nakshatra.
- Forgetting daylight saving time and local mean time.
- Mixing solar-year and 360-day dasha conventions.
A clean answer records the ayanamsa, the time zone, the node convention and the formula used.