How festival dates work
Hindu festivals follow the lunisolar calendar: each is fixed to a tithi (lunar day) in a lunar month, so its date in the Gregorian calendar shifts every year. Astronaad computes the real new and full moons and lunar months from an astronomical ephemeris, then selects the correct day — at sunrise for daytime festivals and pradosh (after sunset) for evening ones like Diwali — verified to the day against the traditional panchang.
Frequently asked questions
- How are Hindu festival dates decided?
- They follow the lunisolar calendar — each festival is fixed to a tithi (lunar day) in a particular lunar month, so its Gregorian date moves each year. Astronaad computes the real new and full moons and the lunar months from an astronomical ephemeris and selects the correct day, verified to the day against the traditional panchang.
- Why do festival dates change every year?
- The lunar year is about 11 days shorter than the solar year, so a festival fixed to a lunar date drifts earlier each year — until a leap (adhika) month resets it. That is why Diwali or Holi land on a different date annually.
- Are the dates the same across India?
- The tithi-based dates are nearly identical nationwide. Some regional festivals and the exact muhurat timings vary slightly by city.