Library
Vedic Astrology Wiki

Tithi Meaning: The 12° Lunar Day and Its Boundaries

Calculate tithi from the Moon–Sun longitude difference. Learn waxing and waning numbering, why a tithi is not 24 hours and how sunrise labels differ.

Names and related terms
Tithi · Lunar day

Editorially reviewed: · Reviewed by OpenFate · Editorial Methodology

Overview

A tithi is a 12° interval in the Moon’s longitude ahead of the Sun, normalized around the zodiac. Thirty tithis form one full 360° cycle. It is an angular lunar day, not a fixed 24-hour civil day or simply the calendar date written beside it.

At a glance

Angle
Moon minus Sun, normalized to 0°–360°
Width
12° per tithi
Fortnights
1–15 waxing;16–30 waning
Duration
Variable; requires finding angle-crossing times

How do I find the tithi number?

Calculate Δ = (Moon − Sun) modulo 360° and use floor(Δ / 12°) + 1. Indices 1–15 belong to the waxing half; 16–30 to the waning half, whose repeated name number is index −15. In the table, waxing 15 is Purnima and waning 15 is Amavasya.

These interval names should not be confused with the exact full-Moon or conjunction instant. In the start-inclusive convention here, exactly 180° begins index 16 and exactly 360° wraps to index 1. Labels such as “full-Moon day” may therefore need the almanac’s sampling convention.

A wrapped difference and a precise boundary

Use invented longitudes Sun 350°, Moon 8°. The raw difference is −342°; adding 360° gives 18°, hence tithi 2. If the Moon advances to 14° while the Sun is fixed for this arithmetic exercise, Δ becomes 24° and tithi 3 begins.

The fixed Sun in this exercise is not an ephemeris forecast. In a real end-time calculation both luminaries move, so solve for their next relative 12° crossing rather than adding a fixed number of clock hours. A monthly date number cannot substitute for that calculation.

Why can almanacs show a repeated or missing tithi date?

A sunrise-based daily heading samples the running tithi at each local sunrise. A tithi lasting across two sampled sunrises can label two days; one beginning and ending between consecutive sunrises may not appear as a sunrise heading. The underlying interval has not disappeared.

Compare the place, sunrise definition and explicit end times before declaring the calendars inconsistent. The same angular tithi can be expressed at different local clock times. No health, financial or relationship outcome is established by the lunar-day number.

Sources and editorial basis

  1. P. V. R. Narasimha Rao: Vedic Astrology — An Integrated Approach
    §1.3.8.1, printed pp. 12–13: 12° lunar-day divisions and waxing/waning names; §1.3.11, p. 17: sunrise-day convention. Formal normalized half-open boundaries and sunrise-sampling examples are editorial exposition, not fixed 24-hour intervals.A named practitioner’s introduction to Jyotish. Used for terminology and a stated method, not universal school agreement or scientific validation. The added March 18, 2010 note describes changed views; it does not establish a fully revised 2010 edition.
  2. OpenFate Editorial Methodology
    OpenFate Editorial Methodology, stable sections #editorial-principles, #editorial-workflow, #editorial-ai, and #editorial-context. Used for the calculation/interpretation and evidence-boundary policy.OpenFate separates deterministic chart calculation, traditional interpretation, and modern editorial explanation.
  3. Swiss Ephemeris Programmer’s Manual: Time, Sidereal Modes and Houses
    Swiss Ephemeris Programmer’s Manual, §12.1 swe_set_sid_mode (including Lahiri modes) and §12.2 ayanamsa functions; §15 house calculation. The page’s rounded arithmetic examples are original teaching inputs, not ephemeris outputs.Primary software documentation for numerical time and position calculations. Sidereal modes, including named Lahiri variants, are explicit settings. The manual does not validate astrological interpretations.
  4. IANA Time Zone Database
    IANA tz database theory.html, “Scope of the tz database” and “Accuracy of the tz database”; historical limitations, especially before 1970. This source does not verify an individual birth record.The maintained source for current and historical civil-time offsets and daylight-saving transitions; it provides timekeeping facts, not astrological interpretation.
  5. OpenFate Vedic implementation: local source review, 2026-09-08
    Read-only local source review: app/modules/vedic/interpretation/forecastFacts.ts module contract and prompt/chat/en.ts §11 prohibit invented transits and use frozen Vimshottari intervals; logic/types.ts records unavailable transit factors; logic/policy.ts lists D1/D2/D6/D9/D10/D24, not D4 or D20. This does not verify deployed screens or demonstrate Panchanga, Muhurta or Sade Sati outputs.An editorial review of local policy and calculation source files, not an independently accessible publication or proof of the deployed version. Implementation limitations and discrepancies remain separate from traditional arithmetic.
Was this article helpful?

Search the Wiki