How the dates are worked out

Every date on this site comes from two steps: the astronomy, and the rule that picks the day.

Astronomical calculations

Sunrise, sunset and the positions of the Sun and Moon are calculated by modern astronomical computation (the Drik method). The site uses Lahiri ayanamsha for sidereal positions. Daily pages identify the location and the times relevant to that day's readings.

To reproduce a result, the date, location, time standard, ayanamsha and rise or set convention must agree. Differences in those choices can explain small differences between calendars.

Observance rules

Festival dates also require a rule for choosing the day. The festival pages state the rule in plain words and explain how it treats the relevant tithi and part of the day.

Pradosham explains the trayodashi rule. Ekadashi discusses the different Smarta and Vaishnava tests. The Yajur Upakarma page shows two rules giving two days, and which one this site follows.

Printed calendars

Calculated festival dates are compared with printed and published calendars before a festival page goes up.

If your calendar gives a different date, write to us with the city, the date and the calendar you use.