Sunrise, sunset and the Vedic day
Sunrise here is the moment the Sun's upper edge clears a sea-level horizon with 34′ of refraction, found to about a tenth of a second at the place's own latitude and longitude; the Vedic day runs from one sunrise to the next.
The day every window of the panchang is measured in.
The Sun's upper limb on the horizon with the standard refraction (34′), at sea level, from the place's coordinates; the same rule as the app's TODAY, checked against Swiss Ephemeris within a minute. Inside the polar circles a day can have no sunrise: then no Vedic day begins there, and the pages say so. The vara (weekday) of a Vedic day is the weekday of its sunrise at the place. "At sunrise here" on each place's page is the tithi running at that place's own sunrise: a tithi between two sunrises has none there, and the day a vrata is kept follows each tradition's rule.