Two Clocks of Tamil Astronomy

The Nazhigai System நாழிகை — சூரிய நாள் கணக்கு

The Nazhigai (நாழிகை) is Tamil astronomy's answer to the question: what time of day is it? It divides the solar day into 60 equal units, each lasting exactly 24 minutes of modern time. The system is purely solar — anchored to sunrise and sunset, governed by the Sun's actual motion, ticking at the same pace every single day regardless of the Moon.

The Structure of 60

Why 60? The number 60 divides cleanly into 1, 2, 3, 4, 5, 6, 10, 12, 15, 20, and 30 — more divisors than any other number of similar size. This makes scheduling and calculation frictionless. The day divides into four watches of 15 nazhigai each, eight sessions of 7.5, or twelve intervals of 5 — always whole numbers.

Sub-divisions: Vinazhigai and Mattirai

The nazhigai itself is subdivided for finer precision. One nazhigai contains 60 vinazhigai (விநாழிகை), and each vinazhigai contains 60 mattirai (மாத்திரை) — giving a three-tier sexagesimal (base-60) system remarkably similar to modern hours, minutes, and seconds.

The Eight Traditional Watches — யாமங்கள்

The Tamil day was also divided into eight yaamas (யாமங்கள்) — watches of 7.5 nazhigai (= 3 hours) each. Four for the day, four for the night. Each watch had a name and purpose — prayer, rest, labour, vigil.

Nazhigai vs Modern Hours

The nazhigai is not an approximation of the hour — it is a different choice. Modern time divides the day by 24 then by 60; the nazhigai system divides by 60 then by 60 again. Both reach the same resolution. The difference is philosophical: Tamil time is always expressed as a fraction of the complete day, not an offset from midnight.

The Tithi System திதி — நிலவின் கட்டக் கணக்கு

While the nazhigai tracks the Sun, the Tithi (திதி) tracks the Moon — specifically, the Moon's angular separation from the Sun as it moves through its monthly cycle. One tithi is the time it takes for this separation to increase by exactly 12 degrees. The result is 30 tithis per lunar month, each one a measurable step in the Moon's eternal dance around Earth.

The Geometry of a Tithi

The Moon completes one synodic cycle — new moon back to new moon — in 29.53059 days. During this time it traverses 360° of angular separation from the Sun. Dividing this by 30 gives 12° per tithi. This is why a lunar month always has exactly 30 tithis, regardless of whether the synodic month is 29 or 30 solar days in a given cycle.

The 30 Tithis: Names and Phases

Each tithi in the 30-day cycle has a name and corresponds to a specific phase of the Moon visible in the sky. The cycle runs from Pratipada (the first day after new moon) through Purnima (full moon on day 15) and back to Amavasya (new moon on day 30).

Why Tithi Has No Fixed Sunrise

Because a tithi is 22 minutes 35 seconds shorter than a solar day, a tithi can begin and end at any solar time. A tithi that starts at sunrise today may start at noon next month, and at midnight the month after that. This is not a flaw — it is the fundamental reason Tamil astronomy kept the two systems entirely separate.

Two Systems, One Cosmos இரண்டு முறைகள் — ஒரே பிரபஞ்சம்

Tamil astronomy did not have to choose between the Sun and the Moon. It measured both, simultaneously, using instruments calibrated to each. The two systems only appear contradictory if you expect one clock to do both jobs.

The 72-Day Connection

The full drift cycle — the number of solar days for a tithi "clock" to complete one full revolution through all solar times — is 72.3 days. This is not unrelated to the 72 years per degree of solar precession: both derive from the same fundamental ratio of tithi-to-solar-year (0.9719). The Tamil number system is self-similar across scales — what holds for a day holds for a century holds for a millennium.