It is common to notice that major observances like Diwali, Karva Chauth, or Nirjala Ekadashi are sometimes celebrated a day apart in different parts of the world. This is not an error in calculation, but a fundamental feature of the Hindu calendar system.
The Sunrise Rule (Udaya Tithi)
In most Vedic traditions, a lunar day (Tithi) is associated with the calendar date on which that Tithi is active at the moment of local sunrise (Udayatithi).
Because sunrise occurs at different Universal Coordinated Times (UTC) across longitudes:
- A Tithi may begin at 05:30 AM IST in New Delhi.
- In London or New York, sunrise occurs hours later or earlier in UTC terms.
- If the Tithi ends before sunrise in New York, the previous Tithi is active at sunrise there, shifting the observance day.
Moonrise Observances (Pradosh & Moon Sighting)
Certain observances depend on specific evening windows rather than morning sunrise:
- Karva Chauth: Fast is broken upon sighting the Moon (Chandra Darshan) during evening hours.
- Maha Shivratri: Rituals take place during Nishita Kaal (midnight window).
Because evening moonrise times vary by latitude and time zone, local moonrise tables must be computed for each city.
The website publishes daily panchang pages for 46 major cities; the app covers 185 and computes the same sunrise rule for whichever city you pin. The date can still shift by a day between those cities — that is the sunrise rule working, not a mismatch.