Before prediction comes calculation
Siddhant Jyotish is India's mathematical astronomy. Here is what it computes, and how you can check it.
Most people meet Jyotish as prediction. Classical students meet it as arithmetic. Jyotish has three branches, and the first, Siddhanta, is astronomy: computing where the planets are, when eclipses fall and how the calendar turns.
Three branches, in order
- Siddhanta: astronomy and calculation.
- Samhita: cycles, omens and collective events.
- Hora: the individual birth chart.
Siddhanta comes first because everything after it depends on it. A chart built on a wrong planetary position is wrong before any interpretation begins.
Ujjain as the prime meridian
Classical Indian astronomers measured longitude from the meridian of Ujjain, the city where Tushar Shukla trained. Sawai Jai Singh II's masonry observatory, the Vedh Shala built in the 1720s, still stands there.
Ayanamsa and precession
Sidereal Jyotish corrects for the slow wobble of Earth's axis, roughly one degree every 72 years. Modern astronomy measures the same precession. This is the part of Jyotish anyone can check against an ephemeris.
Calculation first, interpretation second. That is how the texts are still taught in Ujjain.
Draft explainer, awaiting the author's review before publication.
