01 · 6 min read
What an ephemeris is
An ephemeris is a table of where the planets are — not where tradition says they should be, but where they measurably are, expressed as longitudes along the ecliptic. Every kuṇḍalī, every pañcāṅga entry, every daśā date is downstream of this one table. If the table is wrong, everything built on it is wrong.
Indian astronomy computed such tables for centuries: the Sūrya-Siddhānta gave mean motions, and the Kerala school — Nīlakaṇṭha Somayājī’s Tantrasaṅgraha of 1501 — corrected them with a model that put the five planets on true paths around the Sun. The mathematics was indigenous, rigorous, and testable.
Testable is the key word. A good ephemeris invites you to check it. Ours is checked against NASA’s JPL Horizons on 1,000 stratified dates spanning 2000 to 2050, and the residuals are published to the arc-minute. That is the whole trick: no mystique, just measurement.
Next in this track: how sidereal longitudes differ from tropical ones, and why the ayanāṁśa is the most argued-about number in jyotiṣa.