Shiva

Shiva is the twentieth nityayoga, and its name means auspicious, kindly, and benevolent, the same word names the great god Shiva in his gracious aspect. It is one of the most favourable of the yogas, held excellent for worship, spiritual undertakings, and any work seeking blessing. Reckoned from the summed longitude of Sun and Moon divided into twenty-seven parts, it advances as the lights draw apart. In the panchanga it lends its highly auspicious quality to the reckoning of a muhurta. These are the conventions of the calendar tradition, in which a benefic yoga such as Shiva is sought out for the most important beginnings; the astronomical basis remains the arithmetic of the two luminaries' combined longitude through the lunar month.

Unlike Brahma and Indra, the twenty-fifth and twenty-sixth yogas, which are named for deities associated with creation and kingship respectively, Shiva as the twentieth yoga's name refers to the adjective meaning auspicious or kindly rather than necessarily invoking the god by direct address, though the word is of course also the standard name of the deity himself, and Sanskrit usage does not always sharply distinguish an epithet used as a common adjective from the same word used as a proper name in a given context, so classical commentators occasionally differ on how directly to read a theistic invocation into this particular yoga's naming compared with the more unambiguous Brahma and Indra.

Of the five limbs of the panchanga the yoga is the most purely arithmetical, and the only one a person standing outside at night could never read off the sky. 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. Shiva is the arc from 253 degrees 20 minutes to 266 degrees 40 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 Shiva is the twentieth 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 twentieth position, Purva Ashadha, is where it usually starts.

Shiva sits among the eighteen yogas classed as favourable. That count matters more than it looks: with eighteen of twenty seven benign, the yoga is a weak filter on its own, and the classical muhurta writers use it as a tie breaker between candidate times rather than as a reason to reject one. A day is not made auspicious by its yoga alone.