What is yoga?

Here yoga means “joining.” It refers to joining the two longitudes by addition. This daily calendar quantity, also called nitya-yoga, is not yoga as a spiritual or physical discipline. It is also distinct from the yogas of horoscopic literature, where yoga names a defined combination of astrological factors rather than this daily calendar division.

Nakṣatra: one of 27 sections of the sidereal ecliptic. Aśvinī occupies longitude 0°–13°20′; the Moon’s longitude determines its nakṣatra. In software that longitude is computed from an ephemeris, but it still represents the Moon’s position along the ecliptic.

Yoga: the Sun’s and Moon’s longitudes are added. Complete revolutions are removed from the sum. That resulting number—not either body’s position—is divided into 27 intervals. Viṣkambha is the first, covering values from 0° up to, but not including, 13°20′. These intervals classify a synthetic summed coordinate, not a region of the sky occupied by either body.

Example: Sun 100° + Moon 265° = 365° → 5°, so the sum lies in Viṣkambha. The Sun’s longitude is in Puṣya and the Moon’s is in Pūrvāṣāḍhā; neither body occupies Aśvinī.

Why ayanāṃśa matters: Yoga uses two sidereal longitudes. Because the same ayanāṃśa is subtracted from each, a 1′ difference between ayanāṃśa systems changes the computed yoga sum by 2′ at the same instant. Nakṣatra uses the Moon’s longitude once, while tithi uses the Moon–Sun difference, so ayanāṃśa cancels from the tithi calculation.

Open Pañcāṅga includes all five aṅgas—tithi, vāra, nakṣatra, yoga, and karaṇa. It gives teaching priority to tithi and nakṣatra, along with rāśi, which is not one of the five aṅgas but helps build intuition about longitude. Traditional interpretive uses of yoga are outside the scope of this astronomy-focused guide.