Tritiya

Tritiya is the third tithi of the bright fortnight, when the waxing crescent has grown clearly visible in the western evening sky. It falls in the Jaya group of the fivefold classification, the days associated with victory and gain, and its presiding deity is traditionally the goddess Gauri, a form of Parvati. Several observances attach to it: Akshaya Tritiya, in the bright fortnight of the spring month of Vaishakha, is regarded as one of the most auspicious days of the whole year for beginnings, purchases, and charity, its name meaning the imperishable third. In the panchanga the day is read as favourable and prosperous. These are the conventions of the calendar tradition, laid over the simple astronomical fact of the Moon drawing steadily away from the Sun.

Akshaya Tritiya's name, the imperishable third, reflects a belief that merit earned or gifts given on this tithi does not diminish, a reasoning distinct from the ordinary Purna, Nanda, Bhadra, Jaya and Rikta fivefold classification that grades every tithi's general character; a day can be Jaya by the standard grouping and still be singled out by name for an entirely separate reason tied to a particular festival tradition. Like every tithi, the third's real duration varies with the Moon's changing speed, and the day is one of the small number of tithis in the Hindu calendar, alongside Vijayadashami and the first day of a lunar month in some regional practices, that some almanac traditions treat as swayam siddha, self-auspicious, meaning it does not require an additional check of nakshatra or other panchanga limbs before undertaking major life events such as marriage.

Reckoning a tithi means measuring elongation, the angular distance of the Moon from the Sun, and cutting that circle into thirty equal twelve degree arcs. Tritiya occupies the arc from 24 to 36 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 Tritiya carries Taitila, the fourth, and the second Gara, the fifth. 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 7 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.