Krishna Ekadashi

Krishna Ekadashi is the twenty-sixth tithi overall, the eleventh day of the dark fortnight, and the second of the month's two Ekadashi fasts. Like its bright-fortnight counterpart it is kept as a day of fasting sacred to Vishnu, observed with abstention from grains and beans. In the fivefold grouping it is a Nanda tithi, its deities the Vishvadevas. Particular dark-fortnight Ekadashis carry their own names and merit through the year. The waning crescent is now thin and close to the Sun. The tradition holds both monthly Ekadashis to be among the most meritorious of regular observances, so the fast recurs every fortnight. These are the devotional conventions of Vaishnava practice, resting on the fixed count of eleven days from the full moon.

That the fortnight's second Ekadashi carries the identical devotional weight and fasting obligation as the first, despite falling in the waning rather than waxing half, is itself doctrinally significant in Vaishnava practice: unlike most tithis, where the dark fortnight's instance is treated with more caution than the bright, Ekadashi's sanctity is held to be undiminished by lunar phase, since the fast's purpose, purification and devotion to Vishnu, does not depend on the Moon's light but on the fixed eleven-day count from the preceding full or new moon. Regional traditions differ on precisely which of two possible Ekadashi dates to observe when the tithi spans a calendar-date boundary in a particular way, a live point of disagreement among different Vaishnava lineages and their respective almanacs.

A tithi is not a day. It is an arc, the interval in which the Moon gains twelve degrees of longitude on the Sun, and the civil day merely borrows its name. Krishna Ekadashi occupies the arc from 300 to 312 degrees of that separation. The Moon does not move at a fixed rate, and the same twelve degrees may take a little over nineteen hours near perigee or close to twenty six near apogee. A calendar has to name whole days, so the rule is that whichever tithi is current at sunrise gives the day its name. A tithi shorter than the interval between two sunrises can therefore be skipped entirely, which the tradition calls a kshaya tithi, and one longer than that interval can carry its name over two civil days, an adhika or vriddhi tithi. Both occur in the ordinary course of a year, and both are why an observance can appear on two dates in the same almanac.

Each tithi is halved again, and each half carries a karana, so the first half of Krishna Ekadashi carries Bava, first of the seven movable karanas, and the second Balava, the second movable karana. Seven of the eleven karanas repeat, cycling eight times through the month, while four are fixed to particular half tithis at the month's opening and close.

The Moon is waning through this arc, rising later each night and showing about 21 per cent of the disc lit. The phase follows from the elongation and not the other way round, so the tithi and the shape of the disc are two readings of one measurement.