How we calculate

Every time and date is worked out with astronomy for the place you choose, using the sidereal zodiac with Lahiri (Chitrapaksha) ayanamsha, the standard of the Indian government's Rashtriya Panchang.

• Planet positions: Astronomy Engine (MIT licence), checked against the Swiss Ephemeris to within a minute of time.
• Sunrise and sunset: the top edge of the Sun at the horizon, with standard refraction.
• A panchang day runs from sunrise to the next sunrise; the tithi, nakshatra and yoga at sunrise name the day.
• Months: amanta (new moon to new moon) and purnimanta (full moon to full moon), with adhika (extra) months.
• Festivals follow the common rules for the tithi and time of day (for example Pradosh kaal for Diwali); local customs can differ by a day.
• Rahu kaal, Yamaganda, Gulika and choghadiya: the day (sunrise to sunset) and night are each split into 8 equal parts.