Add the Sun's longitude to the Moon's, divide by 13°20', and you get one of twenty-seven yogas. It is the one almanac quantity that has no equivalent in Western astrology at all.

The tithi is the difference between the two bodies and the yoga is their sum, which means the yoga advances whether the Moon is catching the Sun or leaving it. Each of the twenty-seven has a name and a character, and a handful — Vyatipata and Vaidhriti in particular — are avoided for anything important.