Ekadashi

Ekadashi is the eleventh tithi, and it is the most widely observed of all the lunar days. Occurring twice a month, in both the bright and dark fortnights, it is kept as a fast day sacred to Vishnu; devotees abstain especially from grains and beans from one sunrise to the next. In the fivefold grouping it is a Nanda tithi, and its presiding deities are traditionally the Vishvadevas, the universal gods. The tradition holds the Ekadashi fast to be among the most meritorious of regular observances, and particular Ekadashis through the year carry their own names and stories. The waxing Moon at the bright Ekadashi is nearly full. These are the devotional conventions of Vaishnava practice and the wider calendar, resting on the fixed count of eleven days from new or full moon.

The Vishvadevas, the "all-gods," are a Vedic category of minor deities personifying universal principles rather than a single named figure, and their assignment to Ekadashi reflects the tithi's own comprehensive, all-encompassing devotional weight in Vaishnava practice rather than pointing to any one myth. Because Ekadashi recurs every fortnight, the fast is one of the very few observances in the Hindu calendar kept twice monthly without exception, and different named Ekadashis through the year, Nirjala, Devshayani, Devutthana and many others, are distinguished from one another by the lunar month and fortnight in which they fall, each carrying its own associated story even though the underlying tithi and its Ekadashi fasting rule are identical every time.

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. Ekadashi occupies the arc from 120 to 132 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 Ekadashi carries Vanija, the merchant's karana, and the second Vishti, the karana also called Bhadra. Vishti is the one karana the muhurta literature marks as unfit for beginnings, and its presence in the second half is why this tithi is read with more care than its neighbours. 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 waxing through this arc, setting later each evening and carrying about 79 per cent of the disc lit. That figure is a consequence of the definition rather than an observation added to it: elongation fixes the phase, so naming the tithi already names how much of the disc is lit.