Sunrise in the Panchang (Suryodaya)
In the panchang, the day begins at local sunrise, not midnight. The tithi, nakshatra and other limbs in force at sunrise name the day, and periods such as Rahu Kaal and choghadiya are measured from it.
Also known as: Udaya kala
The Hindu day runs from one sunrise to the next. Whatever tithi is current at sunrise is the day’s tithi (udaya tithi), even if it ends an hour later, and the weekday changes at sunrise too. Daytime periods such as Rahu Kaal, Abhijit muhurat and the day choghadiyas are fractions of the time between sunrise and sunset.
Most modern panchangs take sunrise as the moment the upper edge of the Sun appears on a level horizon, allowing for the way the atmosphere bends light. Some traditional almanacs use the centre of the Sun’s disc, or ignore that bending, which can move sunrise by a few minutes and occasionally shift a tithi or festival by a day.
Because sunrise depends on latitude, longitude and season, timings are local. Rahu Kaal in Chennai differs from Rahu Kaal in Delhi or London on the same date, so a panchang made for another city can mislead. Always use one set to your own location.