Hindu Tithi Converter
Accurate astronomical calculation for Indian Lunar Dates
Understanding the Tithi Calculator
The Hindu calendar, or Panchang, is inherently lunisolar, meaning it tracks the movement of both the Sun and the Moon. Unlike the Gregorian calendar which is purely solar, the Hindu date system relies on “Tithis”. A Tithi is a lunar day, defined scientifically as the time it takes for the longitudinal angle between the Moon and the Sun to increase by 12°.
Because the Moon’s orbit is elliptical and its speed varies, a Tithi can vary in length from approximately 19 to 26 hours. This implies that a Tithi might start at any time of the day and end at any time of the next day, unlike a Gregorian date which always changes at midnight.
How This Tool Works
This Tithi Converter uses advanced astronomical algorithms (based on Jean Meeus’ calculations) to determine the precise positions of the Sun and Moon. It calculates the True Longitude of both bodies, accounting for anomalies like the elliptical orbits and major lunar perturbations.
The formula used determines the difference between the Moon’s longitude and the Sun’s longitude. This result is divided by 12 to find the exact Tithi index. This ensures that you get a mathematically accurate result without relying on static databases or simplified “day-counting” methods which are often inaccurate.
Shukla Paksha vs. Krishna Paksha
The lunar month is divided into two fortnights, known as Pakshas:
- Shukla Paksha (Waxing Phase): The bright fortnight starting from the New Moon (Amavasya) to the Full Moon (Purnima). This is generally considered auspicious for new beginnings.
- Krishna Paksha (Waning Phase): The dark fortnight starting from the Full Moon to the New Moon.
Frequently Asked Questions (FAQ)
1. Why does the Tithi change in the middle of the day?
A Tithi depends on the angle between the Sun and Moon. Since celestial bodies don’t follow a 24-hour clock, a Tithi can begin or end at any specific minute. In Hindu tradition, the Tithi prevailing at Sunrise is usually considered the Tithi for that entire day (Udaya Tithi).
2. How accurate is this calculator?
This calculator uses astronomical algorithms precise to within a few arc-minutes. While sufficient for general purposes, Ekadashi fasting and specific temple rituals may rely on specific “Panchang Siddhanta” (calculation schools) like Drik or Surya Siddhanta, which may differ slightly by location.
3. What is a “Kshaya” or “Vriddhi” Tithi?
Sometimes a Tithi is shorter than the time from one sunrise to the next, causing it to be “skipped” in the calendar list (Kshaya). Conversely, if a Tithi lasts longer than 24 hours and touches two sunrises, it spans two days (Vriddhi).
4. Can I use this for Ekadashi Fasting?
Yes, this tool helps you identify when Ekadashi occurs. However, strict fasting rules (Vrat) often require the Tithi to be present during the “Brahma Muhurta” or require avoiding Dashami overlap. Always consult a local priest for strict Vrat dates.
5. Why do I need to select a Time Zone?
Tithis are universal moments in time, but the “date” they fall on depends on your local sunrise. A Tithi might start on Monday evening in India but Monday morning in New York.