Vishti विष्टि

Vishti is one of the seven movable karanas, which cycle eight times across half-tithis 2 to 57 of every lunar month. It therefore comes round roughly every four days, at any hour — its position is set by the Moon's elongation from the Sun, not by the calendar.

Vishti is Bhadra, and it is the karana muhurat texts single out. All auspicious undertakings are traditionally suspended for its duration: marriage, housewarming, naming ceremonies, journeys, and the start of new ventures. Ongoing work is generally not interrupted.

Because it is movable it recurs eight times a lunar month — about every four days — so it is common enough to be worth checking before fixing any date. Some traditions treat only the portion of Bhadra falling on earth (as opposed to heaven or the underworld, determined by the tithi and paksha) as binding; we show the astronomical span and leave that judgement to you.

A karana is six degrees of the Moon's elongation from the Sun — exactly half a tithi. Every tithi therefore contains two karanas, and every tithi boundary is also a karana boundary. Our engine computes the two independently and asserts they land on the same instant, which is how we know the boundary search is right.