Why the Hindu Day Begins at Sunrise: Solar-Lunar Time Computations

Unlike the Gregorian calendar which turns at midnight, the Hindu civil day (*Ahoratra*) runs from local Sunrise to the subsequent Sunrise.

See sunrise-based calculations for 114 cities on [NaamSetu Panchang](https://panchang.naamsetu.in/panchang).

## The Principle of Udaya Tithi The Tithi in force at the moment of local Sunrise is designated as the *Udaya Tithi* for that entire civil day.

## Handling Tithi Spans (Kshaya & Vriddhi) Because a lunar Tithi (12° angle) varies in real duration (from ~19 to ~26 hours) due to lunar and solar velocity variations: - **Tithi Vriddhi:** A Tithi that touches two consecutive sunrises. - **Tithi Kshaya:** A Tithi that begins after one sunrise and ends before the next, not touching any sunrise directly.