What Is a Tithi? How a Lunar Day Is Calculated
A worked 12-degree example, the difference from a civil day, and why the end time changes from one date to another.
A lunar angle, not a 24-hour date
A tithi is one thirtieth of the synodic lunar cycle in the traditional Panchanga. Rather than starting at midnight, each tithi starts when the apparent ecliptic longitude of the Moon minus that of the Sun crosses a successive multiple of 12 degrees. These boundaries are moments in time, not blocks of 24 clock hours.
Suppose the Moon has longitude 108° and the Sun 90° in a consistent coordinate system. Their separation is 18°, inside the second tithi, whose interval is 12° up to but not including 24°. When that separation reaches 24°, the third tithi begins; the example gives an angle, not a real-time forecast for today.
Why a tithi can be short or long
Both bodies move along the ecliptic, and the Moon’s angular speed is not constant. The time needed for the Moon–Sun separation to increase by 12° therefore varies; a tithi can begin and end during the same civil date or span parts of two dates. Thirty tithis make one complete cycle of elongation, but they are not thirty equal solar days.
The name shown for a festival date may also follow a sunrise-based observance convention. That is a separate question from asking which tithi is astronomically active at 14:00. A reliable calendar should make the selected tradition and its local transition times visible instead of using one daily label as though nothing changes.
How to read it in Galaxiora
Choose your city and a date in Panchanga, then inspect the current tithi together with its end time. If you plan an activity in the afternoon, check whether a transition happens before it starts. Compare with the nakshatra and other relevant calendar factors; a tithi by itself cannot certify the whole occasion.
Write down the civil date, local time zone, tithi number and transition instant if you compare two websites. A mismatch between local display times may be a time-zone difference rather than an astronomical disagreement. The site’s practical advantage is a city-specific display, not a promise that the symbolic interpretation is scientifically predictive.
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Sources and methodology
References for checking the astronomical and calendrical facts in this guide. Traditional interpretations are not astronomical measurements.