Krishna Shashthi

Krishna Shashthi is the twenty-first tithi overall, the sixth day of the dark fortnight, sharing the character of the sixth tithi and its dedication to Kartikeya or Skanda, the war-god. In the fivefold grouping it is a Nanda or joyful tithi. The waning Moon by this day is near its last quarter, rising around midnight. While the great Skanda festivals fall in the bright fortnight, the sixth tithi of the dark half carries his associations too, and regional observances vary. These are the conventions of the calendar and festival tradition, in which the character of a tithi follows its number across both fortnights while its auspicious weight is modulated by whether the Moon is waxing or waning.

Because the great Skanda festivals cluster in the bright fortnight, principally the six-day cycle culminating in Skanda Shashthi itself, the dark-fortnight Shashthi has comparatively little independent festival literature of its own, and its main significance in most panchangas is simply as the sixth tithi of the waning half carrying the standard Nanda classification and Kartikeya's general association rather than any specific named observance. This asymmetry, where one fortnight's instance of a tithi accumulates rich festival tradition while the other largely does not, recurs across several numbered tithis in this list and reflects the historical accident of which month and fortnight particular festivals happened to become fixed to, rather than any rule governing bright versus dark observance generally.

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 Shashthi occupies the arc from 240 to 252 degrees of that separation. Since lunar motion quickens and slackens across the month, the arc is crossed in as little as about nineteen hours or as much as about twenty six. The panchanga settles the mismatch by naming each civil day for the tithi in force at its sunrise. 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 Shashthi carries Gara, the fifth, and the second Vanija, the merchant's 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 70 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.