Vajra

Vajra is the fifteenth nityayoga, and its name means the thunderbolt, the diamond-hard weapon of Indra. It is one of the inauspicious yogas, associated with sudden, forceful, and disruptive events, and the panchanga counts it among the configurations to be avoided for auspicious beginnings. Like the others it is found from the combined longitude of Sun and Moon divided into twenty-seven equal parts. The malefic yogas such as Vajra are set aside when an astrologer chooses a muhurta, the tradition reading them as periods of abrupt shock. These are the conventions of the calendar tradition, which fixes the character of each yoga; the astronomical basis remains the arithmetic of the two luminaries' summed longitude through the lunar month.

Vajra, the thunderbolt, is also the diamond in Sanskrit, the same word covering both the weapon of Indra and the hardest known substance, an association the tradition explains by the thunderbolt's supposed indestructibility, and the word gives its name to the Vajrayana, the thunderbolt vehicle, a major branch of Buddhist practice centred on Tibet and the Himalayan region that takes the vajra as one of its central ritual implements and symbols. The nityayoga's own association with sudden, forceful disruption draws on the weapon sense of the word rather than the diamond sense, though both meanings were current together throughout the period the astrological terminology was fixed.

A yoga is arrived at by addition, which sets it apart from every other reckoning in the almanac. Where the tithi measures the Moon's separation FROM the Sun, the yoga measures the two longitudes ADDED together, and cuts the resulting circle into twenty seven equal arcs of thirteen degrees twenty minutes. Vajra is the arc from 186 degrees 40 minutes to 200 degrees 00 minutes of that sum. The sum climbs at roughly fourteen degrees ten minutes a day, so a yoga runs about twenty two and a half hours on average, a little shorter than a tithi, and like a tithi it can be skipped between two sunrises or carried across two of them.

The twenty seven arcs are the same width as the twenty seven nakshatras, and Vajra is the fifteenth arc of the grid in both schemes, which is why the two are often tabulated side by side. They are not the same thing and share nothing but their arithmetic: a nakshatra is a segment of the sky the Moon is physically standing in, while a yoga is a number derived from two positions and belongs to no part of the sky at all. Reading a yoga as a star group is the commonest confusion the term invites, and the shared name of the fifteenth position, Swati, is where it usually starts.

Vajra sits among the nine yogas classed as unfavourable. Nine of twenty seven is a third of the cycle, so an inauspicious yoga is a common event rather than a rare one, and the muhurta literature treats it accordingly: it weighs against a time without ruling it out, and is routinely overridden where the tithi, the nakshatra and the weekday agree.